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OF  THE 


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W.  A..  ROEBLING. 

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Brooklyn 


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ENGINEER  JOHN  A.  ROEBLING 


PNEUMATIC 


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OF  THE 


EAST  RIVER 


Pension  brw66- 


W.  A^.  ROEBLING. 

18  7  3. 

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AVERELL   &    PECKETT,    Printers,   20    &    22   Gold  Street. 


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avi;ry  Architectural  and  fine  arts  library 

Gift  of  SEYMOUR  B.  DURSl  Old  York  Library 


PREFACE 


The  following  pages  comprise  chiefly  the  annual  reports 
on  the  progress  of  the  East  River  Suspension  Bridge,  from 
1869  to  1872.  f 

Having  heretofore  appeared  in  newspaper  form  only,  they 
are  now  presented  as  a  connected  narrative,  giving  a  detailed 
account  of  the  work  from  its  inception  to  the  present  time, 
when  the  foundations  are  finished  and  the  towers  have  already 
reached  more  than  half  their  intended  height.  They  present, 
a  history  of  the  successful  completion  of  the  two  largest 
pneumatic  foundations  extant,  as  regards  area  of  base, 
although  surpassed  in  depth  by  those  of  St  Louis. 

Being  the  first  application  of  timber  caissons  on  a  large 
scale,  it  may  be  of  interest  to  state,  that,  at  the  time  of  writ- 
ing, with  already  more  than  two-thirds  of  the  ultimate  pres- 
sure on  the  base  of  the  Brooklyn  tower,  the  total  settle 
ment  has  only  been  five-eighths  of  an  inch,  and  of  uniform 
character  all  around. 

An  introductory  chapter  is  added,  giving  an  outline  of  the 
general  plan  of  the  structure,  its  principal  dimensions  and 
location,  as  originally  designed  by  the  late  John  A.  Roebling, 
and  described  by  him  in  his  preliminary  report  of  1867  ;  to- 
gether with  the  few  modifications  made  since  then. 

Brooklyn,  Oct.  1st  1872. 


INTRODUCTORY  REMARKS. 


The  East  River  Bridge  will  form  a  suspended  highway, 
connecting  New  York  and  Brooklyn,  cities  of  respectively 
one  million,  and  four  hundred  thousand  inhabitants.  The 
location  of  the  terminus  in  New  York  is  opposite  the  City 
Hall,  in  Chatham  street ;  and  in  Brooklyn,  in  the  square 
bounded  by  Fulton,  Sands,  Washington,  and  Prospect  streets, 
comprising  a  total  length  of  five  thousand  nine  hundred  and 
eighty-nine  feet.  It  forms  an  air  line  from  the  City  Hall  to 
the  square  above  mentioned. 

Of  this  whole  length,  three  thousand  four  hundred  and 
fifty-five  feet  are  suspended  in  three  main  openings.  The 
central  span  will  cross  the  river  from  pier-line  to  pier-line, 
without  impeding  navigation,  in  one  single  span  of  one 
thousand  five  hundred  and  ninety-five  feet,  six  inches,  from 
centre  to  centre  of  tower.  From  each  tower  towards  the 
land  side,  half-spans  will  be  supported  by  the  land  cables, 
nine  hundred  and  thirty  feet  long  each,  measuring  from  the 
centre  of  tower  to  face  of  anchor-wall. 

From  the  face  of  the  anchor-wall,  on  the  New  York  side,  a 
distance  remains  of  one  thousand  five  hundred  and  sixty-two 
feet,  six  inches,  to  Chatham  street,  and  from  the  anchor-wall 
to  the  Brooklyn  terminus,  a  distance  of  nine  hundred  and 
seventy-one  feet. 

These  distances,  between  the  anchorages  and  termini,  are 
known  as  the  approaches.  These  latter  will  be  supported  by 
iron  girders  and  trusses,  and  will  rest  at  short  intervals  upon 
small  piers  of  masonry  or  iron  columns,  located  within  the 
blocks  of  buildings  which  will  be  crossed  and  occupied. 
These  pillars  will  form  part  of  the  walls  needed  for  the  di- 
vision of  the  occupied  ground,  into  stores,  dwellings,  or 
offices. 


6 


INTRODUCTORY  REMARKS. 


In  every  such  case  the  bridge  floor  will  be  constructed 
fire  and  water  proof ;  serving  as  a  roof  to  the  blocks  of  houses 
underneath.  The  streets  will  be  crossed  by  iron  girders  and 
trusses,  twelve  in  number. 

There  will  be  one  uniform  grade  of  three  feet,  three  inches 
per  one  hundred  feet  from  the  New  York  terminus  to  the 
centre  of  the  Bridge,  and  the  same  from  the  Brooklyn  ancho- 
rage. That  of  the  Brooklyn  approach  will  be  less,  only  two 
feet,  nine  inches  per  one  hundred  owing  to  the  greater  eleva- 
tion of  the  terminus. 

The  roadway  will  pass  the  towers  at  an  elevation  of  one 
hundred  and  nineteen  feet,  and  in  the  centre  of  the  main 
span,  the  elevation  in  the  clear  of  the  lower  chord  of  the 
Bridge,  will  be  one  hundred  and  thirty-five  feet  above  mean 
high  water,  or  one  hundred  and  forty  feet  above  low  water. 

This  elevation  was  fixed  by  special  Act  of  Congress,  being 
an  increase  of  five  feet  over  that  of  the  original  plan. 

It  is  sufficient  to  permit  the  unobstructed  passage  of  all 
schooners,  barques,  brigs  and  steamers,  as  well  as  ships  below 
a  thousand  tons.  Ships  above  that  tonnage  will  have  to  lower 
their  upper  spars.  The  amount  of  such  tonnage  is  however 
only  one-tenth  of  that  passing  under  the  Bridge,  and  the 
number  of  such  vessel  not  one  in  two  hundred,  diminishing 
moreover  in  numbers  from  year  to  year,  as  the  commerce  of 
•the  world  is  carried  on  more  and  more  by  steamers. 

The  suspended  superstructure  will  consist  of  an  iron  fram- 
ing eight)- -five  feet  in  width  from  out  to  out,  suspended  from 
four  main  cables  by  wire  rope  suspenders  attached  to  iron 
floor-beams,  which  are  placed  seven  feet  six  inches  apart. 
The  flooring  is  further  divided  into  five  spaces  by  six  lines 
of  iron  trusses,  of  which  the  two  centre-lines  have  a  depth 
of  twelve  feet,  and  the  others,  of  eight  feet ;  the  lower  chords 
being  placed  below  the  iron  floor  beams. 

The  outer  spaces  have  a  width  in  the  clear  between  the 
truss  posts  of  eighteen  feet,  one  inch,  and  accommodate  each, 
two  lines  of  iron  tramways  for  ordinary  vehicle  travel,  as  well 
as  for  street  cars,  drawn  either  singly,  by  horses,  or  in  pairs, 
by  light  dummies.    The  next  two  spaces  are  thirteen  feet  two 


INTRODUCTORY  REMARKS. 


7 


inches  wide  each,  provided  with  iron  rails  for  the  running 
of  two  passenger  trains  back  and  forward  alternately. 

These  trains  will  be  attached  to  an  endless  wire-rope,  pro- 
pelled by  a  stationary  engine,  which  is  located  on  the  Brook- 
lyn side,  underneath  the  floor,  the  two  tracks  being  operated 
like  an  incline  plane,  with  a  speed  of  twenty  miles  per  hour, 
the  whole  transit  occupying  only  five  minutes  from  terminus 
to  terminus. 

From  eight  to  ten  compartment  cars,  each  fifty  feet  long, 
and  holding  one  hundred  persons,  will  constitute  a  train. 
By  means  of  opposite  doors  on  the  side  of  the  cars,  and  wide 
platforms,  it  is  possible  to  fill  and  empty  the  trains  in  two 
minutes,  without  producing  interference  between  the  going 
and  coming  passengers.  For  this  reason  the  Bridge  is 
widened  out  to  one  hundred  feet  at  this  point. 

In  addition  to  these  trains,  arrangements  are  being  made 
for  a  connection  with  the  underground  railroad,  (New  York 
Central)  at  the  New  York  City  Hall,  by  which  passenger 
cars  can  be  passed  over  the  Bridge  to  Brooklyn  without 
change.  These  cars  will  pass  under  Chatham  street,  and  be 
transferred  to  the  level  of  the  Bridge  by  a  hydraulic  lift. 

The  Central  or  fifth  division  of  the  Bridge  floor  forms  a 
promenade  for  foot  travel,  fifteen  feet  in  width.  It  is  eleva- 
ted five  feet  above  the  roadway,  affording  a  view  over  both 
sides  of  the  Bridge. 

Cables. 

The  Bridge  is  supported  by  four  main  cables  ;  two  outer 
ones,  and  two  near  the  middle  of  the  flooring.  They  will  be 
sixteen  inches  in  diameter;  composed  of  galvanized,  tem- 
pered, cast  steel  wire,  No.  6  gauge  ;  having  a  strength  of  one 
hundred  and  sixty  thousand  pounds  per  square  inch  of  sec- 
tion. The  cables  are  aided  by  a  system  of  one  hundred  and 
four  stays  in  each  quarter.  They  together  will  uphold  the 
superstructure  of  the  main  span,  the  aggregate  weight  of 
which,  inclusive  of  cables,  will  be  five  thousand  tons. 

Towers. 

The  two  main  towers  form  the  principal  features  of  the 


8 


I N TRODUCTOKY  R E M ARKS. 


work.  At  the  water-line  the  New  York  tower  has  a  length 
in  the  direction  of  the  river  of  one  hundred  and  forty-one 
feet,  and  a  width  of  fifty-nine  feet.  On  top  of  the  timber 
foundation  these  dimensions  are  respectively  one  hundred 
and  fifty-seven  feet,  and  seventy-seven  feet,  while  the  base  of 
the  foundation  measures  one  hundred  and  seventy-two  feet 
by  one  hundred  and  two  feet. 

The  elevation  of  the  floor  is  one  hundred  and  nineteen  feet 
above  high  water  ;  the  height  of  the  roofing  above  the  floor, 
one  hundred  and  forty-nine  feet,  making  a  total  height  of 
two  hundred  and  sixty-eight  feet  from  high  water  to  the 
roof,  without  balustrade  ;  or  from  the  base  of  the  foundation 
to  top  of  the  balustrade  three  hundred  and  fifty-four  feet. 
The  towers  consist  essentially  of  three  main  shafts,  united 
below  the  floor  line  by  connecting  walls,  the  latter  enclosing 
two  square,  hollow  spaces  for  the  purpose  of  saving  masonry. 
Above  the  floor  these  shafts  extend  singly  for  a  height  of 
eighty  feet  ;  here  they  are  united  by  two  gothic  arches  of 
thirty-six  feet  rise,  covering  the  roadways. 

The  facestone  throughout  are  Granite,  and  the  backing 
also,  with  the  exception  of  a  small  portion  of  Limestone. 
The  backing  throughout  is  cut  backing,  thus  reducing  the 
spaces  occupied  by  cement  and  concrete  to  less  than  8  per 
cent. 

The  quantity  of  masonry  in  the  New  York  tower  from  the 
timber  to  the  summit  is  44,000  yards,  giving  a  weight  of 
about  93,000  tons  on  top  of  the  timber  foundation,  super- 
structure included.  These  quantities  do  not  include  the 
timber  and  concrete  foundation  below  the  masonry.  Includ- 
ing the  latter  we  have  a  pressure  at  the  base  of  the  entire 
structure  of  six  and  a-half  tons  per  square  foot.  On  top  of 
the  timber,  ten  tons  ;  on  the  masonry  at  the  water  line, 
thirteen  and  a-half  tons,  and  at  the  base  of  the  Central  Shaft 
at  the  Floor  line,  twenty-six  tons ! 

To  meet  these  exceptionally  great  pressures,  the  masonry 
has  throughout  been  laid  in  the  most  conscientious  manner, 
and  all  by  day's  work. 




9 


The  Anchorages 
Will  each  contain  33,000  yards  of  masonry.  No  rock  being 
available,  it  is  necessary  to  provide  artificial  foundations,  ex- 
tending to  the  water  level  with  an  excavation  of  twenty  feet, 
that  in  Brooklyn  consisting  of  a  timber  platform,  and  that  in 
New  York  of  piles.  The  Anchorage  forms  a  mass  of  stone, 
one  hundred  and  twenty-nine  feet  by  one  hundred  and  nine- 
teen feet  at  the  base,  and  one  hundred  and  seventeen  by  one 
hundred  and  four  at  the  top.  The  height  is  eighty-nine  feet 
above  the  river,  it  being  necessary  to  carry  it  up  to  the  grade 
of  the  floor. 

The  four  cables  enter  the  masonry  at  an  elevation  of  eighty- 
two  feet,  and,  after  passing  into  the  wall  for  twenty-five  feet, 
they  form  a  connection  with  the  chains.  The  latter  consist 
of  cast  steel  bars,  thirteen  feet  long  and  ten  inches  wide,  by 
one  and  a-half  inches  thick,  arranged  in  ten  sections,  each 
containing  nineteen  bars  and  forming  in  all  four  curved  lines 
extending  from  the  cables  to  the  anchor-plates.  The  con- 
nections are  made  by  six  inch  steel  pins. 

The  four  anchor-plates  are  located  at  the  base  of  the 
masonry.  They  consist  of  casting,  oval  in  outline,  with 
radial  arms,  having  a  dimension  of  nineteen  feet  by  seven- 
teen feet,  and  depth  of  three  feet,  weighing  twenty -five  tons 
each.  The  arrangement  of  the  anchor  walls  is  such  as  to 
have  two  large  spaces  in  each,  eighty  feet  long  by  twenty 
feet  wide,  and  divided  into  six  stories,  serving  for  ware- 
houses above  and  for  an  underground  railway  passage  in  the 
lower  story. 

In  March,  1869,  the  financial  affairs  of  the  Company  were 
placed  upon  such  a  basis  as  to  warrant  the  commencement  of 
the  preliminary  operations  usually  connected  with  such  a 
work.  A  board  of  Consulting  Engineers  were  convened  at 
the  request  of  Mr.  John  A.  Roebling,  with  the  object  of  ex- 
amining into  the  general  feasibility  of  the  work  and  making 
a  report  thereon.  Its  members  consisted  of  Messrs.  Allen, 
Latrobe,  Kirkwood,  McAlpine,  Adams,  Steele,  and  Serrel. 
Their  deliberations,  substantially  endorsing  the  plans,  are 
contained  in  a  report  written  by  the  President  of  the  Board, 
Mr.  Horatio  Allen. 


10 


INTRODUCTORY  REMARKS. 


In  May,  1869,  a  commission  of  three  Government  Engi- 
neers, General  Wright,  General  Newton,  and  Major  King, 
were  appointed,  by  the  War  Department,  in  compliance 
with  an  act  of  Congress,  to  report  upon  the  East  River 
Bridge,  in  regard  to  its  being  an  obstruction  to  navigation 
as  well  as  upon  the  general  feasibility  of  the  project. 

Those  gentlemen  recommended  an  increase  of  five  feet  in 
the  elevation  of  the  floor  of  the  main  span  of  the  Bridge, 
fixing  it  at  one  hundred  and  thirty-five  feet  above  mean  high 
spring  tides. 

In  order  to  avoid  the  increase  in  grade  caused  by  this 
additional  elevation,  and  also  to  save  the  increased  amount 
of  masonry  in  towers  and  approaches,  which  would  have 
entailed  an  extra  expense  of  $300,000  ;  it  was  determined  to 
overcome  it  by  making  an  entire  change  in  the  plan  of  the 
superstructure,  throwing  the  trusses  altogether  above  the 
floor  in  place  of  partly  above  and  partly  below  as  contem- 
plated in  the  original  plan.  At  the  same  time  the  floor  of 
the  Bridge  was  widened  from  eighty  to  eighty-five  feet,  to 
accommodate  two  double  tracks  for  vehicles  in  place  of  two 
single  tracts.  The  Government  Commission  also  decided 
that  no  part  of  the  permanent  masonry  of  the  towers  above 
water  should  extend  beyond  the  pier  lines,  and  that  no  part 
of  the  foundation  of  the  towers  should  extend  above  the  na- 
tural bed  of  the  river,  beyond  the  pier  line.  In  June  work 
was  commenced  on  the 

Surveys. 

The  general  line  known  as  the  park  route  had  before  been 
determined  on,  but  no  actual  line  had  ever  been  located 
upon  the  ground,  the  proposed  line  having  simply  been 
traced  upon  the  best  maps  procurable.  Several  centre  lines 
were  run  on  trial.  The  one  finally  fixed  upon  narrow  lv 
escapes  the  Fulton  Ferry  slip  on  the  Brooklyn  side,  and  the 
Williamsburgh  Ferry  on  the  New  York  shore,  being  re- 
stricted at  the  same  time  to  the  two  termini  fixed  by  the 
charter. 

In  the  location  of  most  bridges  some  attention  is  paid  to 
the  difficulties  likely  to  be  incurred  in  getting  foundations 


INTRODUCTORY 


REMARKS. 


for  piers,  in  making  approaches,  etc.  ;  but  here  such  con- 
siderations had  to  be  ignored,  and  the  towers  and  anchor- 
ages placed  wherever  the  exigencies  of  the  case  brought 
them. 

A  minute  and  detailed  survey  of  all  the  property  on  the 
line  of  the  Bridge  was  then  made  and  the  location  of  the 
Brooklyn  tower  fixed  upon.  This  work  consumed  most  of 
the  Summer  months  of  1869. 

It  was  while  engaged  in  locating  the  position  of  the 
Brooklyn  tower  that  Mr.  John  A.  Roebling  met  with  a 
lamentable  accident — the  crushing  of  his  right  foot  by  the 
shock  of  a  ferry  boat  against  the  fender  rack  of  spring  piles 
on  which  he  was  standing.  Lock-jaw  speedily  set  in,  and 
after  sixteen  days  of  extreme  suffering,  terminated  in  death. 

For  a  period,  operations  on  the  bridge  came  to  a  stand 
still. 

In  August,  the  writer  was  appointed  Chief  Engineer  of 
the  work.  The  Executive  Committee  of  the  Bridge  Com- 
pany, were  likewise  empowered  to  proceed  with  the  neces- 
sary steps  for  securing  the  site  of  the  Brooklyn  foundation, 
making  a  contract  for  the  caisson,  and  preparing  the  site  for 
its  reception.  Mr.  Horatio  Allen  was  appointed  consulting 
Engineer  during  the  foundation  work,  and  to  Messrs.  Webb 
&  Bell,  of  Greenpoint,  was  awarded  the  contract  for  building 
and  launching  the  timber  caisson. 


THE  BROOKLYN  FOUNDATION. 


One  trial  boring,  made  in  1867,  showed  gniess  rock  at  a 
depth  of  ninety-six  feet  below  high  water.  The  strata  pene- 
trated consisted,  besides  the  surface  filling,  principally  of 
hard  pan  and  alternate  layers  of  trap  boulders  imbedded  in 
sand  and  clay.  Below  a  depth  of  fifty  to  sixty  feet  the  ma- 
terial was  so  compact,  that  the  bore  hole  stood  without 
tubing  for  weeks.  No  necessity  existed  therefore  for  going 
down  to  rock,  since  a  depth  of  fifty  feet  would  suffice. 

But  the  great  desideratum  to  be  attained  was  a  founda- 
tion of  a  uniform  character  over  the  entire  space,  whatever 
the  depth  might  be.  It  is  well  known  that  the  drift  forma- 
tion of  Long  Island  presents  a  great  variety  of  strata  in 
comparatively  short  distances.  Within  a  few  hundred  feet 
on  either  side  of  this  foundation,  there  is  no  bottom  so  to 
speak,  and  piles  are  driven  a  great  depth  into  the  mud, 
whereas  in  the  centre  of  our  foundation  the  depth  was  only 
a  few  feet ;  the  existing  ferry  slip  had  been  blasted  out  at 
great  expense,  and  to  drive  an  iron-shod  pile  even  two  feet 
into  that  material,  was  the  work  of  hours. 

This  hard  material,  however,  occupied  only  a  part  of  the 
foundation  which  comprises  an  area  of  seventeen  thousand 
square  feet.  One  third  of  this  area,,  towards  the  East,  was 
much  softer  in  character. 

To  meet  the  requirements  of  this  case  a 

Solid  Timber  Foundation 

Was  decided  upon,  of  sufficient  thickness  to  act  as  a  beam, 
and  having  the  requisite  mass  to  insure  uniform  settling. 
The  importance  of  a  uniform  foundation  becomes  evident 


14 


THE   BROOKLYN  FOUNDATION. 


when  we  consider  the  size  of  the  tower,  weighing  seventy 
thousand  tons,  with  a  height  (if  three  hundred  feet  above 
the  foundation  upon  which  the  permanent  pressure  is  five 
tons  per  square  foot. 

The  buoyancy  of  the  timber  moreover  enables  us  to  dis- 
pense with  the  use  of  screws,  commonly  employed  in  lower- 
ing caissons. 

Again,  in  regard  to  durability,  it  is  well-known  that  tim- 
ber immersed  in  salt  water  is  imperishable,  and  to  protect 
it  against  sea-worms,  it  is  merely  necessary  to  sink  it  beneath 
the  river  bed.  It  therefore  at  once  suggested  itself  to  make 
this  timber  platform  as  much  as  possible  a  part  of  the 

Caisson. 

This  has  been  done  by  making  the  roof  of  the  caisson  a 
solid  mass  of  timber,  of  fifteen  feet  in  thickness.  The  object 
and  purpose  of  a  caisson  in  sinking  a  pneumatic  foundation 
are  already  too  well  known  to  require  any  special  descrip- 
tion, it  is  merely  a  diving  bell  on  a  vast  scale. 

The  caisson  of  the  Brooklyn  foundation  is  a  large  inverted 
vessel  or  pan,  resting  bottom  upward,  with  strong  sides. 
Into  this  air  is  forced,  under  a  sufficient  pressure  to  drive 
out  the  water.  Entrance  is  had  to  the  large  working 
chamber  thus  formed  underneath,  through  suitable  shafts 
and  air  locks.  The  excavated  material  is  taken  out  through 
water  shafts,  open  above  and  below,  and  two  supply  shafts 
send  down  the  material  subsequently  needed  to  fill  up  the 
air  chamber.  A  few  smaller  pipes  are  also  inserted  for  a 
variety  of  purposes, 

The  dimensions  of  the  caisson  are  rectangular,  length  one 
hundred  and  sixty-eight  feet,  width  one  hundred  and  two 
feet,  height  of  air  chamber  nine  feet  six  inches,  and  thickness 
of  roof  before  launching,  five  feet.  The  sides  form  a  V  and 
are  nine  feet  thick  where  they  join  the  roof,  sloping  down 
to  a  round  edge.  The  inner  slope  of  the  V  has  an  angle  of 
forty-five  degrees.  The  cutting  edge  or  shoe  is  formed 
by  a  semi-circular  casting  protected  by  a  sheet  of  boiler- 
plate, extending  up  three  feet  on  the  sides. 


THE   BROOKLYN  FOUNDATION. 


*5 


A  heavy  oak  sill,  two  feet  square,  rests  directly  on  this 
casting.  The  succeeding  three  courses  are  laid  lengthwise, 
of  yellow  pine.  After  that  the  alternate  courses  are  heading 
courses.  The  whole  V  is  thoroughly  held  together  by  drift- 
bolts  and  screw-bolts.  In  addition  there  are  heavy  angle 
irons,  uniting  the  V  to  the  roof.  At  the  principal  corners 
the  courses  of  timber  are  halved  into  each  other  and  strapped 
together. 

The  immediate  roof  is  composed  of  five  courses  of  twelve- 
inch  square  yellow  pine  sticks,  laid  close  together,  bolted 
sideways  and  vertically,  and  having  a  set  of  bolts  running 
through  the  whole  of  the  five  courses.  The  outer  face  of 
the  caisson  has  a  batter  inward  of  one  foot  in  ten,  to  facili- 
tate its  descent  into  the  ground. 

To  make  the  caisson  air-tight,  the  seams  were  all 
thoroughly  caulked  for  a  depth  of  four  inches  inside  and 
out.  In  addition,  a  vast  sheet  of  tin,  unbroken  throughout, 
extends  over  the  whole  caisson,  between  the  fourth  and  fifth 
courses,  and  down  the  four  sides  to  the  shoe.  The  tin  on 
the  outside  is  further  protected  by  a  sheathing  of  yellow 
pine.  The  space  between  the  timbers  was  filled  with  hot 
pitch  and  grout.  As  air  under  a  pressure  of  forty  or  fifty 
pounds  will  penetrate  wood  with  ease,  the  inside  of  the  air- 
chamber  was  coated  with  an  air-tight  varnish,  made  of  rosin, 
menhaden  oil,  and  Spanish  brown.  The  air-tightness  pro- 
duced by  these  means  has  throughout  proved  quite  satis- 
factory. 

The  yellow  pine  timber  used  in  construction,  came  princi- 
pally from  Georgia  and  Florida.  Its  average  weight  was 
forty-eight  pounds  per  cubic  foot,  although  many  sticks 
were  so  heavy  as  to  sink  in  water.  All  bolt-holes  bored  into 
this  timber  have  a  drift  one-eighth  inch  to  insure  a  good 
hold.    No  bolts  were  used  with  ragged  ends. 

Shafts. 

The  water  shafts,  two  in  number,  are  rectangular  in. section, 
seven  feet  by  six  feet  six  inches,  made  of  three-eighths  inch 
boiler  plate,  properly  stiffened  by  angle-irons,  and  secured 
to  the  caisson  timber.    These  shafts  are  open  above  and 


i6 


TIIK    BROOKLYN  FOUNDATION. 


below,  the  lower  edge  extending  tw«ity-one  inches  below 
the  edge  of  the  shoe.  The  water  within  them  rises  and 
falls  with  the  state  of  the  tide  outside. 

The  material  to  be  removed  is  shoved  under  the  lower 
edge  into  the  pool  of  water  underneath,  and  is  then  taken 
out  by  the  clam-shell  dredge  of  Messrs.  Morris  &  Cum- 
mings,  of  New  York. 

This  instrument  is  a  self-acting  grapnell,  possessing  nearly 
the  same  functions  as  the  human  hand  in  picking  up  and  dis- 
charging material.  Any  other  arrangement  for  excavating 
in  the  shape  of  a  revolving  dredge,  or  a  sand  pump,  was  out 
of  the  question.  The  air-shafts  are  two  in  number,  three 
feet  six  inches  in  diameter,  and  simply  extend  through  the 
timber  inside  of  the  well  holes,  the  lock  being  placed  on  top 
of  the  timber,  below  the  ultimate  water  level.  At  the  bottom 
of  the  air-shaft  is  an  additional  door,  hanging  down  into  the 
chamber,  and  enabling  us  to  use  the  whole  shaft  as  a  lock. 
The  supply  shafts  or  pipes,  two  in  number,  are  twenty-one 
inches  in  diameter,  and  pass  through  the  timber,  extending 
two  feet  into  the  chamber  below,  and  carried  up  above  the 
water  level.  They  have  a  door  above  and  below,  and  an 
equalizing  pipe.  When  charged  with  material,  the  com- 
pressed air  is  admitted,  the  lower  door  falls  open,  and  the 
contents  fall  into  the  chamber. 

Divisions  of  Air-Chamber. 

It  was  the  original  intention  to  have  made  the  air-chamber 
under  the  caisson  one  entire  space,  without  any  division 
into  compartments,  thus  facilitating  the  excavation  of 
material.  The  roof  was  strong  enough  for  this  arrange- 
ment. Various  considerations,  however,  led  to  the  aban- 
donment of  that  view.  Since  the  caisson  was  to  be  launcJied 
like  a  ship,  a  certain  number  of  launching  ways  were  re- 
quired, combined  with  a  stiff  frame,  from  the  launching  way 
to  the  roof. 

Again,  in  such  a  boulder  soil,  only  a  few  points  of  the 
edge  would  be  touching  at  once,  and  would  have  to  support 
the  whole  weight  above.  But  the  chief  point  was  the  rise 
and  fall  of  the  tides,  and  their  effect  upon  the  caisson.  This 


THE    BROOKLYN  FOUNDATION. 


rise  and  fall  amounts  in  the  extreme  to  seven  feet  six  inches. 
If  the  inflated  caisson  were  just  barely  touching  at  high 
water,  it  would  press  upon  the  supports  with  a  force  of  four 
thousand  tons  at  low  water,  all  of  which  had  to  be  met  by 
the  strength  of  the  edges  and  frames,  there  being  no  side 
friction  as  yet. 

The  air-chamber  was,  therefore,  divided  into  six  rooms 
by  five  dividing  frames.  These  frames  form  a  heavy  truss 
of  pine  posts  and  stringers,  with  side  sheathing  and  side 
braces  to  the  roof  every  six  feet,  and  are  proportioned 
according  to  the  strains  in  the  launching.  The  ends  of  the 
frames  are  secured  to  the  sides  of  the  caisson  by  knees. 

The  Launch. 

It  was  concluded  to  limit  the  pressure  of  the  caisson  dur- 
ing the  launch  to  two-and-a-half  tons  per  square  foot  of 
launching  surface.  This  required  seven  ways  in  all,  two 
under  the  edges  and  five  under  the  frames.  The  total 
launching  weight  was  3,000  tons,  comprising  11 1,000  cubic 
feet  of  timber,  and  250  tons  of  iron. 

The  launch  was  arranged  sideways,  that  is,  with  the  long 
face  of  one  hundred  and  sixty-eight  by  fourteen  feet  six 
inches  high  towards  the  water.  The  groundways  were  laid 
at  an  angle  of  one  inch  per  foot,  the  caisson  standing  fifty 
feet  back  from  the  end  of  the  ways.  In  order  to  buoy  up 
the  forward  end  of  the  structure,  as  it  entered  the  water, 
and  thus  prevent  its  entire  immersion,  a  temporary  water- 
tight compartment  was  put  in,  one-third  of  the  whole  width. 
It  served  its  purpose  admirably.  A  full  complement  of 
wheelbarrows,  crabs,  winches,  and  other  tools,  were  like- 
wise placed  within  for  future  use. 

The  groundways  consisted  of  two  timbers  eleven  inches 
square,  bolted  together  sideways.  They  were  grooved  like 
the  guide  of  a  planer,  the  upper  launchingway  fitting  them 
correspondingly,  only  the  outer  ways  were  provided  with 
ribbands. 

The  great  danger  to  be  apprehended  in  launching  so  large 
a  mass  on  saven  ways,  consisted  in  the  liability  of  one  end 


[8 


THE   BROOKLYN  FOUNDATION. 


going  faster  than  the  other,  and  thus  wedging  the  caisson 
fast  on  the  ways.  This  was  obviated  by  the  V  shaped  groove 
of  the  groundway,  and  placing  the  ribbands  on  the  inside  of 
the  outer  ways.  In  order  to  gain  an  accelerating  speed,  the 
ways  were  laid  crowning  to  the  extent  of  eighteen  inches. 
The  launchingways  also  extended  ten  feet  back  of  the  caisson 
and  were  provided  with  shores  resting  against  its  sides.  It 
was  desirable  that  the  rear  edge  of  the  caisson  should  leave 
the  ends  of  the  groundways  simultaneously,  and  not  stick 
fast  on  one,  a  thing  likely  to  occur,  unless  prevented  by  the 
above  arrangement. 

On  the  19th  of  March,  1 870,  the  haunch  took  place.  It  was  a 
success  in  every  respect ;  as  soon  as  the  last  block  was  split 
out  the  caisson  began  to  move.  The  impetus  it  had  acquired 
in  the  first  part  of  its  course  proved  sufficient  to  overcome 
the  immense  resistance  offered  by  the  water.  The  air  caught 
inside  of  the  air-chamber,  assisted  materially  in  buoying  up 
during  the  launch.  Neither  the  battering  rams  provided  to 
start  her,  nor  the  checks  to  hold  her  back,  were  needed. 
The  deck  was  not  submerged,  neither  was  the  wave  of  trans- 
lation in  front  very  large. 

An  air-pump  and  boiler  had  been  set  up  on  deck  before 
launching.  These  were  at  once  put  in  motion,  and  in  a  few* 
hours  the  water  was  all  displaced  from  the  air-chamber,  the 
air  blowing  out  at  one  corner,  thus  proving  a  satisfactory 
state  of  tightness. 

When  the  air  was  afterwards  allowed  to  escape  entirely, 
the  top  of  the  caisson  settled  down  within  seventeen  inches 
of  the  water,  which  happened  to  agree  with  previous  calcu- 
lation. When  inflated,  the  caisson  remained  quite  level, 
owing  to  the  balancing  power  of  the  heavy  timber  sides  of 
the  air-chamber. 

The  whole  of  the  launching  arrangements,  as  well  as  the 
responsibility  of  the  entire  launch,  rested  with  the  builders, 
Messrs.  Webb  &  Bell,  who  deserve  the  greatest  praise  for 
the  successful  manner  in  which  they  carried  out  so  novel  a 
work.  They  accomplished  the  result  by  simple  common 
sense  arrangements ;  no  money  was  wasted  upon  elaborate 
precautions  or  fancied  contingencies. 


THE    BROOKLYN  FOUNDATION. 


'9 


Preparing  the  Site  of  the  Foundation. 

It  has  been  estimated  that  the  same  length  of  time  would 
be  required  to  prepare  the  bed  for  the  caisson  as  to  build  it. 
But  owing  to  some  unforseen  difficulties,  possession  of  the 
ground  was  not  obtained  until  January  i,  1870. 

The  winter  had  hitherto  been  mild  and  continued  so,  much 
to  our  advantage. 

The  preparation  of  the  site  consisted  in  establishing  a  rec- 
tangular basin,  open  towards  the  water  side,  surrounded  on 
three  sides  by  a  wall  of  sheet  piling  with  the  bottom  levelled 
off  to  a  uniform  depth  of  eighteen  feet  below  high  water. 
This  point  was  determined  upon  because  one  portion  of  the 
bottom  was  already  as  deep,  and  because  the  caisson  required 
that  much  water  to  come  in  at  all  stages  of  the  tide. 

The  dismantling  of  this  space — the  ferry  slip — drawing  a 
hundred  piles,  tearing  out  three  hundred  and  fifty  feet  of 
fender  sheathing,  removing  the  same  amount  of  heavy  crib- 
bing filled  with  stone,  and  dredging  off  the  loose  material 
on  top,  required  in  all  about  one  month. 

The  dredging  was  performed  by  the  Osgood  dredge,  and 
the  piles  drawn  by  a  craneboat.  One-half  of  the  pier  sepa- 
rating the  Fulton  Ferry  slip  from  our  inclosure  was  also  re- 
moved without  interfering  with  the  Ferry. 

All  the  timber  and  piles  taken  out  were  found  to  be  infested 
with  thousands  of  sea  worms  ;  their  ravages,  however,  were 
bound  to  be  confined  to  the  space  between  low  water  and  the 
mud  line.  A  pile  which  was  sixteen  inches  diameter  below 
the  mud  perfectly  sound  and  free  from  worms,  would  be 
found  eaten  away  to  a  thin  stem  of  three  inches  just  above  ; 
all  timber,  moreover,  being  affected  alike. 

This  experience  shows  the  necessity  of  going  below  the 
river  bed  with  the  timber  foundation,  and  also  proves  its 
entire  safety  in  that  position. 

Dreihiing  and  Blasting. 

In  all  there  were  ten  thousand  seven  hundred  yards  taken 
out — the  bulk  of  it  in  the  course  of  a  month — comprising  the 
filling  in  and  surface  mud.    A  line  of  soundings  then  taken 


• 


20 


THK 


I5KOOK.I ,YN  VO  V  N I ) ATI ( >N . 


showed  three  thousand  yards  yet  to  be  removed  before  the 
level  of  eighteen  feet  was  reached. 

The  character  of  this  material  was  next  to  solid  rock,  as 
none  of  the  dredges  could  make  the  slightest  impression  on 
it  ;  neither  the  Osgood  nor  the  powerful  grapnel  of  Morris 
&  Cummings.  All  the  old  harbor  charts  indicated  this  point 
to  be  a  reef  of  rocks  or  boulders,  subsequently  covered  by 
filling  from  the  shore. 

Under  these  circumstances,  recourse  was  necessarily  had 
to  powder.  Surface  blasting  was  not  resorted  to  because  the 
locality  forbade  the  use  of  heavy  charges,  which  are  essential 
for  success.  A  surface  charge  of  less  than  three  hundred 
pounds  would  have  been  of  no  effect  at  all. 

It  was  determined  to  make  holes  in  the  bottom  of  four  or 
five  feet  in  depth,  by  means  of  a  six-inch  iron  pile,  driven  in 
and  then  withdrawn.  Into  these  holes  a  cannister  containing 
twenty  pounds  of  powder  was  inserted  by  a  driver,  the  pile- 
driver  was  then  withdrawn,  and  the  charge  exploded  by  elec- 
tricity. The  result  was,  a  small  crater  and  the  loosening  of 
the  contiguous  boulders.  Three  such  piles  were  used, 
twenty-two  feet  long,  and  shod  with  iron  at  point  and  head. 

Two  pile  drivers  were  coupled  together  for  this  work,  and 
a  double  gang  of  laborers  employed  day  and  night,  under 
charge  of  Captain  Scott.  A  week's  practice  reduced  the 
matter  to  a  system,  and  developed  the  kind  of  cannister  to  be 
used,  the  exploders  and  the  battery.  From  the  ordinary  tin 
cannister  we  passed  to  lapwelded  tubes,  cut  in  lengths  of  two 
feet,  and  plugged  at  each  end.  They  proved  very  effective, 
but  the  supply  getting  scarce,  recourse  was  had  to  cast-iron 
shells,  with  sides  one-half  inch  thick.  These  possessed  the 
additional  advantage  of  dropping  to  the  bottom  of  the  hole 
of  their  own  weight.  The  average  number  of  blasts  made 
with  one  gang  was  thirty-five ;  the  greatest  delay,  however, 
was  experienced  in  withdrawing  the  iron  piles  from  the 
ground,  which  frequently  resisted  the  united  efforts  of  two 
sets  of  triple  blocks,  worked  by  two  engines. 

The  batter)-  used  was  a  small  frictional  machine,  enclosed 
in  a  light  rubber  case,  and  supplied  by  the  Oriental  Co.  of 


THE    BROOKLYN    FOUNDATION.  21 


Boston,  who  also  furnished  the  exploders.  This  machine 
was  instantaneous  in  its  effects,  never  out  of  order,  and 
would  set  off  any  number  of  charges  at  the  same  time. 

After  a  thorough  blasting,  the  Osgood  dredge  could  work 
to  advantage  for  a  time.  Boulders,  too  heavy  for  the  dredge, 
were  slung  under  water  by  divers,  and  either  raised  or  floated 
under  water  beyond  the  enclosure.  The  whole  process  was 
expensive  but  effective. 

Nature  of  Bottom. 

This  driving  of  iron  piles  afforded  a  thorough  knowledge 
of  the  entire  ground.  On  the  eastern  side  a  few  blows  would 
force  the  pile  through  soft  clay  to  a  depth  of  forty  feet,  where 
it  was  brought  up  by  a  hard  stratum.  In  the  centre,  how- 
ever, there  was  a  broad  ridge  of  hard  pan  of  varrying  thick- 
ness and  so  hard  that  frequently  one  hundred  blows  of  a 
one  thousand  five  hundred  pound  hammer  were  required  to 
drive  the  pile  three  feet  into  the  material.  Towards  the 
south  side,  the  clay  again  disappeared,  giving  place  to  large 
boulders,  packed  close  together,  a  coarse  sand  filling  up  the 
spaces.  On  the  water  side,  all  sand  or  clay  was  washed 
away,  leaving  the  bare  stone. 

As  time  passed  along,  all  work  was  confined  to  the  line  of 
frames  and  edges  alone,  leaving  the  ridges  between  to  be 
removed  afterwards  from  under  the  caisson.  Three-fourths 
of  the  boulders  removed  were  of  Trap,  with  a  few  of  Gneiss 
and  sandstone. 

No  dredge  ever  built  is  adapted  for  such  work.  Ordinary 
dredge  buckets  present  too  much  surface  for  penetration, 
and  for  similar  work  should  be  replaced  by  a  single  tooth, 
so  made  as  to  plow  up  the  material.  This  was  tried  with 
some  success. 

The  cost  of  dredging  the  soft  material  on  top  was  sixty 
cents  per  yard;  but  of  the  hard  material  below,  including 
blasting,  $3.62  per  yard.  One  thousand  one  hundred  and 
seventy-three  blasts  were  fired,  consuming  thirteen  thou- 
sand pounds  of  powder. 

While  the  dredging  progressed,  the  enclosure  proceeded, 


22 


TIIK    BROOKLYN  FOUNDATION. 


an  outer  row  of  piles  was  first  driven,  and  anchored  back 
with  timber,  to  resist  the  pressure  of  a  bank  of  twenty-two 
feet,  within  this  line  a  row  of  sheet  piling  was  placed,  space 
being  allowed  to  tow  in  the  caisson. 

Machinery. 

During  April,  six  air-compressing  machines  were  placed 
on  their  foundations  and  satisfactorily  tested.  They  were 
manufactured  by  the  Burleigh  Rock  Drill  Co.  of  Fitchburg, 
Mass.  Each  engine  is  20  horse  power,  and  drives  two  single 
acting  air-cylinders  of  fourteen  inch  stroke,  and  fifteen  inch 
diameter.  Every  engine  has  its  own  boiler,  and  they  are  all 
so  connected  that  the  stoppage  of  no  one  boiler  or  engine 
will  effect  the  rest. 

A  large  condensing  vessel  serves  to  precipitate  the  mois- 
ture in  the  compressed  air,  and  deliver  dry  air  into  the 
caisson.  The  compressed  air  is  cooled  in  the  air  pumps 
themselves,  by  the  injection  of  a  fine  spray  of  water  into  the 
cylinder,  with  every  stroke  of  the  pump. 

A  ten  inch  main,  one  hundred  and  fifty  feet  in  length, 
leads  the  air  underground  to  the  caisson,  where  its  branches, 
and  two  rubber  hose  of  six  inches  diameter,  lead  the  air 
to  the  supply  shafts,  and  thus  into  the  caisson.  Self-acting 
clack' valves  prevent  escape  of  air  in  case  of  accident  to  the 
hose,  which,  however,  had  all  been  tested  to  a  pressure  of 
sixty  pounds. 

The  double  steam  engines  were  set  up  on  the  land  side  to 
operate  the  dredge  buckets  in  the  water-shafts,  and  two 
engines  at  each  end  of  the  caisson  for  operating  the  stone 
sitting  machinery. 

Towing  the  Caisson  into  position. 

By  May  first,  the  leveling  off  of  the  site  had  proceeded 
far  enough  to  bring  the  caisson  down  from  Greenpoint,  a 
distance  of  five  miles.  Advantage  had  been  taken  of  the 
delay  to  put  on  two  more  timber  courses  and  also  to  make 
a  contract  with  the  builders  to  finish  the  remaining  ten  ad- 
ditional courses  of  yellow  pine. 


THE    BROOKLYN  FOUNDATION. 


23 


The  caisson  was  towed  down  by  six  tugboats,  under  charge 
of  Captain  Maginn.  During  the  trip  the  air-pump  was  kept 
in  operation  and  the  air-chamber  fully  inflated,  so  that  the 
air-rushed  out  under  one  corner.  The  great  buoyancy  pos- 
sessed by  the  V-shaped  sides  prevented  any  tilting.  This 
inflation  was  essential,  as  in  one  part  of  the  river  there  was 
but  a  foot  of  space  between  the  bottom  and  the  lower  edge 
of  the  caisson. 

The  trip  was  made  in  two  stages,  on  account  of  the  tides. 
On  the  second  day  the  caisson  was  warped  into  place  with- 
out any  trouble,  and  immediately  secured  by  a  roll  of  piling 
in  front,  which  served  to  support  a  track  for  stone  cars. 

By  the  twentieth  of  June  the  ten  courses  of  timber  were 
laid.  They  cross  each  other  at  right  angles,  with  spaces  of 
lour  to  five  inches  between  the  sticks.  At  every  intersection 
the  stick  is  fastened  by  a  seven-eighth  inch  drift-bolt.  The 
whole  mass  is  thus  bound  together  into  one  unyielding  plat- 
form. The  amount  of  timber  laid  in  five  weeks  amounted  to 
over  one  hundred  thousand  cubic  feet.  The  spaces  between 
are  filled  in  with  concrete,  which  serves  to  add  to  the  neces- 
sary weight,  as  well  as  to  harden  and  preserve  the  timber. 

As  the  courses  were  built  up,  the  outer  ends  were  stepped 
back,  and  covered  with  concrete,  forming  a  mass  five  feet  in 
thickness,  serving  to  protect  it  against  worms. 

Additional  sections  of  water-shafts  and  air-shafts  were  put 
on,  and  an  air  communication  established  through  the  supply 
pipes. 

The  air-locks  are  seven  feet  high,  and  six  feet  six  inches 
diameter  inside.  The  sides  are  of  half-inch  boiler  plate,  and 
heads  of  cast-iron  :  six  bull's  eyes  light  up  the  interior.  To 
avoid  the  lengthening  out  of  the  air-shafts,  the  locks  are 
placed  on  top  of  the  timber  within  water-tight  compart- 
ments, which  occupy  the  spaces  of  the  well-holes  in  the 
towers,  and  will  keep  out  the  water  when  the  timber  is  sub- 
merged. The 

Masonry 

Is  laid  by  means  of  three  large  dericks  with  horizontal 


24  THE    BROOKLYN  FOUNDATION. 

booms,  standing  on  the  caisson  itself,  and  guyed  from  the 
land.    They  control  all  parts ol  the  foundation. 

For  the  lower  courses,  the  Kingston  limestone  was  used, 
furnished  by  Noon  &  Madden.  These  stone  have  both  beds 
cut,  but  the  sides  and  builds  left  rough  with  vertical  quarry 
joints.  The  beds  are  exceptionally  wide.  As  the  base  of 
the  masonry  resting  on  the  timber  is  very  much  larger  than 
the  section  of  masonry  at  the  water  level,  it  is  considered 
that  this  class  of  work  is  equally  as  good,  and  certainly  far 
cheaper  than  regular  dimension  stone.  All  the  stone  in  a 
course  are  cut  to  a  uniform  rise.  The  latter  varying  from 
two  feet  to  two  feet  four  inches. 

Above  low  water,  granite  is  used  exclusively  for  face- 
stone. 

In  connection  with  the  masonry,  a  large  stone-yard  has 
been  established,  three  miles  below  the  bridge,  provided 
with  fourteen  derricks  for  piling  up  stone,  and  three  double 
steam  engines  for  unloading.  The  yard  has  a  capacity  of 
fifteen  thousand  yards.  As  the  stones  arrive  from  the 
quarries  in  sailing  vessels  or  barges,  they  are  unloaded  and 
assorted  in  courses,  and  then  reloaded  upon  stone  scows,  of 
which  seven  have  been  built,  and  sent  to  the  tower.  The 
cutting  is  all  done  at  the  quarries. 

Work  in  the  Air-Chamber. 

On  the  iothof  May,  1870,  the  air-chamber  was  first  entered 
and  explored.  Bv  degrees,  as  the  masonry  was  put  on,  and 
the  caisson  settled  more,  the  force  of  workmen  was  in- 
creased. 

The  removal  of  the  temporary  wooden  compartment,  as 
well  as  pushing  all  loose  material  out  under  the  edges,  and 
cutting  door-ways  through  the  main  division  frames  was 
accomplished  in  due  time. 

Several  weeks  were  occupied  in  removing  trap  boulders 
which  happened  to  come  under  the  frames  and  edges.  The 
removal  of  such  stone  from  under  the  edge,  imbedded  as 
they  were  in  clay,  and  containing  often  one  hundred  cubic 


THE   BROOKLYN  FOUNDATION. 


25 


feet  in  mass,  was  a  matter  of  difficulty  and  patience,  en- 
hanced moreover  by  a  deposit  ot  two  feet  of  slimy  dock 
mud. 

During  this  period  we  had  to  contend  with  the  rising  of 
the  caisson  at  every  high  tide,  and  its  resting  on  the  ground 
again  at  low  water.  This  required  the  inside  work  to  be 
clone  at  low  tide,  when  the  air-chamber  was  comparatively 
free  from  water.  Some  time,  therefore,  elapsed  before  the 
cutting  edge  was  sufficiently  imbedded  in  the  hard  ground 
to  shut  off  direct  communication  with  the  water  outside. 
Moreover,  since  the  shape  of  the  shoe  is  rounding,  it  allows 
the  air  to  blow  out  before  the  water  inside  has  reached  its 
lowest  limit ;  this  is  caused  by  any  trifling  agitation  of  the 
level  of  the  water  inside,  which  gives  the  escaping  air  a 
chance  to  establish  an  outgoing  current  before  the  head  of 
water  inside  becomes  great  enough  to  overcome  it. 

In  proportion  as  weight  was  placed  on  top  of  the  caisson, 
without  any  corresponding  sinking  of  the  structure,  the  cen- 
ter of  gravity  was  raised  and  a  condition  of  unstable  equilib- 
rium established.  One  end  of  the  caisson  would  remain  on 
the  ground,  while  the  other  alone  would  rise  with  the  tide, 
the  level  of  the  water  inside  being  of  course  governed  by  the 
higher  edge  of  the  chamber. 

This  circumstance  was  attended  by  another  phenomenon 
of  imposing  appearance.  The  rising  of  the  end  would  not 
be  gradual,  but  amount  suddenly  to  six  inches  or  more.  The 
result  is  that  for  a  few  minutes  the  tension  of  the  air  inside 
exceeds  the  head  of  water  inside,  and  a  tremendous  outward 
rush  of  air  takes  place  under  the  shoe,  carrying  with  it  a 
huge  column  of  water  to  a  height  of  sixty  feet  at  times.  This 
continues  until  the  return  wave  inside  the  caisson  checks  it. 
Such  blow-offs  are  not  felt  to  any  extent  by  the  men  inside, 
beyond  the  warning  noise  and  momentary  draft  created. 

The  magazine  of  force  contained  in  one  hundred  and  sev- 
enty thousand  cubic  feet  of  air,  is  so  large  that  the  loss  of  a 
few  hundred  tons  of  it  is  a  trifle. 


26 


Til K    BROOKLYN  FOUNDATION. 


Excavation  of  Material. 

Three  courses  of  masonry  were  sufficient  to  prevent  any 
further  rise  from  the  effects  of  the  tide.  By  this  time  the 
force  of  men  had  been  increased  to  over  one  hundred,  and 
work  could  be  carried  on  continuously. 

Although  the  preliminary  dredging  had  arrived  at  a  uni- 
form level  of  eighteen  feet  below  high  tide,  there  had  been 
enough  boulders  overlooked  to  reduce  this  to  sixteen  and 
one-half  feet.  Several  weeks  were  occupied  in  removing 
boulders  and  reducing  the  level  to  eighteen  feet,  before  the 
excavating  machinery  was  ready.  In  the  pits  under  the 
water  shafts  were  several  large  boulders,  below  the  inner 
water  level,  upon  which  the  lower  edge  of  the  shafts  rested. 
These  were  a  source  of  considerable  anxiety,  until  removed 
by  the  tedious  process  of  chipping  them  to  pieces  with  long 
steel  bars. 

The  material  now  became  sufficiently  exposed  to  enable 
us  to  arrive  at  the  conclusion  that  it  was  of  a  very  formid- 
able nature,  and  could  only  be  removed  by  slow,  tedious, 
and  persistent  efforts.  This  had  indeed  been  the  expectation, 
from  our  previous  experience  in  the  dredging  and  blasting 
under  water.  But  the  work  being  under  water,  and  there- 
fore out  of  sight,  did  not  impress  us  so  much  at  the  time,  as 
now  when  we  were  face  to  face  with  it. 

Nature  of  Material. 

In  the  two  middle  chambers  of  the  caisson  the  ground 
was  composed  of  trap  boulders,  large  and  small  packed  to- 
gether so  closely  as  to  touch,  the  space  between  being  filled 
by  a  natural  concrete,  composed  of  decomposed  fragments 
of  green  serpentine  rock.  The  boulders  were  coated  with 
this  natural  cement,  which  adhered  so  strongly  as  to  defy 
the  action  of  steel  wedges.  A  steel  pointed  pick  had  no 
effect  whatever.  It  was  only  by  using  a  steel  pointed  crow- 
bar, and  driving  it  in  the  crevices  with  heavy  sledges,  that 
any  of  this  material  could  be  piled  up  and  removed.  In 
chambers  No.  one  and  two  adjoining  the  Fulton  ferry  slips 
the  boulders  were  equally  as  large  and  as  numerous,  but  the 


THE    BROOKLYN  FOUNDATION. 


27 


cementing  material  was  clay  and  gravel,  not  as  hard  as  the 
serpentine  concrete.  In  chamber  Nos.  five  and  six,  however, 
this  hard  ridge  rapidly  fell  away,  giving  place  to  several 
feet  of  mud,  underlaid  by  a  stratum  of  unctuous  blue  clay, 
and  continuing  soft  in  the  north  corner  of  No.  six  chamber, 
for  a  depth  of  fort)-  feet  as  had  been  indicated  by  previous 
soundings. 

It  was  evident,  therefore,  in  order  to  have  a  uniform 
foundation  over  the  entire  area  of  the  caisson,  it  would  be 
necessary  to  go  down  fully  forty  feet,  and  this  depth  was 
extended  to  forty-five  feet,  so  as  to  have  the  timber  entirely 
below  the  river  bed. 

The  area  of  the  caisson,  seventeen  thousand  square  feet, 
is  so  large  that  no  uniform  stratum  over  the  whole  surface 
would  be  likely  to  be  found  anywhere  within  this  drift 
formation  at  any  moderate  depth  below  the  water  level. 
No  better  foundation  could  have  been  wished  for  than  that 
found  in  chambers  Nos.  three  and  four  provided  it  had  ex- 
tended all  over. 

Nine-tenths  of  the  boulders  were  trap,  transported  hither 
during  the  drift  period  from  the  Palisades  of  the  Hudson. 
Owing  to  their  hardness  they  had  resisted  the  wear  of  time 
the  longest.  They  occured  of  all  sizes,  from  one  cubic  foot 
up  to  two  hundred  and  fifty.  Boulders  of  quartz  and  gneiss 
rock  occurred  more  rarely.  Two  large  boulders  of  red 
sandstone  were  also  found.  The  softer  varieties  of  rocks 
had  all  been  worn  out  to  pebbles.  A  collection  made  of 
the  various  specimens  encountered  during  the  descent  of 
the  caisson  presents  a  complete  series  of  the  rocks  found  for 
a  hundred  miles  to  the  north  and  northeast  of  Brooklyn. 

Lowering  the  Caisson. 

The  adoption  of  a  regular  system  for  lowering  the  caisson 
uniformly  was  a  matter  of  much  experiment  at  the  beginning. 
No  amount  of  pressure  could  force  the  bearing  surfaces  of  it 
through  the  ground  without  crushing  the  cast-iron  shoe  at 
the  cutting  edge,  or  mashing  the  bearing  frames.  A  few 
days'  experience  demonstrated  that  fact.     On  the  contrary. 


28  THE    BROOKLYN  FOUNDATION. 


it  became  a  matter  of  primary  importance  to  dislodge  all 
boulders  in  advance,  before  the  shoe  or  the  frames  came  to 
a  bearing  upon  them. 

All  this  work  had  to  be  done  under  water,  because  there 
was  usually  along  the  shoe  a  vrench  filled  with  water  com- 
municated with  the  water  outside,  and  this  trench  was  con- 
nected with  cross-trenches  under  the  frames,  which  in  time 
supplied  the  large  pools  around  the  water  shafts. 

The  finding  of  these  boulders  in  advance  was  a  laborious, 
disagreeable,  never-ending  task.  Its  performance  fell  entirely 
upon  the  engineering  staff  in  the  caisson,  Col.  Paine  and  Mr. 
Clark.  The  perimeter  of  the  shoe  or  cutting  edge  measures 
about  five  hundred  and  forty  feet,  adding  to  this  the  five 
frames  of  one  hundred  and  two  feet  each,  gives  a  total  length 
of  one  thousand  and  fifty  lineal  feet  of  bearing  surface,  every 
inch  of  which  had  to  be  carefully  probed  under  water  twice 
a  day  with  a  steel  sounding  bar,  and  the  proper  conclusions 
drawn  as  to  the  best  means  of  moving  the  rocks,  hard-pan, 
and  other  material  found.  Each  shifting  gang  of  laborers 
had  to  be  informed  anew  whenever  their  turn  of  work  came 
on.  Being  under  water,  this  beside  became  a  matter  of 
memory  and  not  of  mere  eyesight.  Moreover,  a  settling  of 
the  caisson  of  six  inches  or  a  foot,  would  bring  to  light  an 
entirely  fresh  crop  of  boulders  in  new  positions,  and  very 
often  halt  without  and  half  within  the  caisson. 

The  shoe  being  of  necessity  unsupported,  it  was  left  for 
the  frames  to  support  so  much  of  the  weight  of  the  caisson 
as  was  not  balanced  by  the  air-pressure. 

The  first  attempt  in  the  operation  of  lowering  was  to  leave 
small  pillars  of  earth  under  the  frames,  about  three  feet 
square,  and  from  six  to  eight  feet  apart,  the  intervening  earth 
being  taken  away,  and  forming  part  of  the  trench.  These 
pillars  were  to  be  then  uniformly  undermined,  and  the  cais- 
son lowered  in  that  manner.  It  was  so'on  found  that  the  pil- 
lars usually  concealed  the  head  of  a  large  boulder,  which  re- 
quired their  premature  removal.  Again,  the  water  would 
wash  them  down,  and  still  oftener  the  laborers  in  adjacent 


THE    BROOKLYN  FOUNDATION. 


29 


chambers,  not  working  in  unison,  would  undermine  them 
and  destroy  their  effect. 

The  plan  next  adopted  worked  very  well,  and  was  pursued 
to  the  end.  It  consisted  in  supporting  the  frames  every  eight 
feet  on  two  wooden  blocks,  twelve  inches  square  and  two 
feet  long,  one  above  the  other,  with  four  stout  oak  wedges 
interposed  between  the  blocks  and  bottom  of  the  frame.  A 
continuous  trench,  two  leet  deep  and  four  feet  wide,  was  thus 
maintained  under  the  frames,  giving  ample  working  room 
for  the  removal  of  boulders.  Whenever  the  shoe  had  been 
cleared  out  for  six  inches  in  advance,  these  wedges  were  then 
loosened  with  sledge  hammers,  one  by  one,  and  frame  by 
frame,  until  the  caisson  slowly  settled.  Then,  either  new 
blocks  were  put  in  of  a  smaller  size  alongside,  or,  as  was 
usually  the  case,  they  were  allowed  to  crush.  Very  often  a 
sudden  descent  of  the  caisson  would  crush  half  the  bearing 
blocks,  until  brought  up  by  the  shoe.  The  operation  was 
analogous  to  the  splitting  out  ot  blocks  and  wedges  during 
the  launch  of  a  ship. 

The  bottoms  of  the  frames  were  originally  two  feet  wide. 
This  width  was  found  too  great  to  allow  of  the  easy  removal 
of  rocks  from  underneath.  They  were,  therefore,  cut  down 
to  a  width  of  one  foot.  The  lower  ends  of  the  frames  were 
likewise  cut  loose  from  the  side  of  the  caisson,  to  allow  more 
easy  access  to  the  point  of  junction.  This  reduction  of  bear- 
ing surface  added  materially  to  the  risk  in  case  of  accident. 

Removal  of  Boulders  and  Earth. 

Boulders  occurring  inside  of  a  chamber  were  usually  left 
undisturbed  until  the  caisson  had  sunk  sufficiently  to  enable 
us  to  attack  them  above  the  water  level.  They  were  then 
split  into  manageable  blocks  by  plug  and  feather. 

Boulders  under  the  frame  presented  more  difficult}-.  The 
ground  in  which  they  were  imbedded  was  cut  awav  with 
steel  bars  as  much  as  possible  ;  they  were  then  drilled  under 
water,  and  a  lewis  inserted.  The  appliances  for  pulling  them 
out  of  their  beds  were  various.  Those  first  in  use  consisted 
of  double  sets  of  block  and  tackle,  aided  by  winches  and  crow- 


THE    BROOKLYN  FOUNDATION. 


bars,  with  a  gang  of  thirty  or  forty  men  hauling  at  the  ropes. 
All  this  force  was  frequently  found  ineffective.  The  strain 
required  being  usually  from  two  to  three  times  the  weight 
of  the  stone.  The  cause  of  this  lay  in  the  air  pressure  which 
amounted  not  only  to  the  fifteen  pounds  of  atmospheric 
pressure  but  the  caisson  pressure  in  addition,  the  whole 
being  effective  by  reason  of  the  watertight  clay  in  which  the 
stone  was  embeded.  As  soon  as  the  boulder  was  loosened 
in  its  bed  to  a  slight  extent,  it  soon  followed.  These  hauling 
arrangements  were  replaced  after  a  time  by  three  of  Dud- 
geon's Hydraulic  pulling  jacks,  two  of  ten  tons  and  one  of 
fifteen  tons  capacity.  This  proved  to  be  a  very  effective  in- 
strument. They  were  usually  attached  to  heavy  screw  bolts 
let  into  the  roof  of  the  caisson  and  formed  part  of  a  chain 
leading  to  the  stone.  Many  boulders,  however,  resisted  the 
united  efforts  of  all  three  jacks. 

The  removal  of  the  hard  earth  could  be  effected  at  the  be- 
ginning only  by  the  use  of  steel-pointed  crow-bars  driven  in 
with  sledge  hammers.  Under  water  the  blow  of  a  pick  has 
but  little  effect.  The  long  handled,  round  pointed  shovel 
answered  best  for  lifting  the  material  out  of  water  into  wheel- 
barrows 

After  the  caisson  had  been  lowered  about  two  feet  it  be- 
came possible  to  build  dams  around  the  trenches  under  the 
frames  and  bail  out  the  water.  This  enabled  us  to  see  the 
work  at  hand,  and  materially  lightened  the  labor  attending 
it.  These  dams  were  shifted  from  trench  to  trench,  care  being 
taken  always  to  leave  an  open  trench  leading  to  the  water  shaft. 

The  removal  of  the  water  from  the  trenches  was  accom- 
plished partly  by  hand-bailing,  then  by  air  syphon  pumps 
and  steam  syphon  pumps,  and  finally  by  the  compressed  air 
itself,  throwing  it  entirely  outside  of  the  caisson  through 
pipes  introduced  through  the  timber  and  masonry. 

To  work  the  air  syphon  a  complete  system  of  one  and  a- 
half  inch  pipes  was  placed  in  the  caisson  with  suitable  con- 
nection. Through  this  pipe  air  was  introduced  under  a 
pressure  of  sixty  pounds,  one  of  the  main  air  pumps  being 
set  apart  for  that  purpose.  The  pump  was  constructed  on 
the  principle  of  a  Giffard  injector,  and  as  the  duty  required 


THE   BROOKLYN  FOUNDATION. 


31 


was  simply  to  lift  the  water  from  three  to  four  feet  it  was 
expected  to  work  well,  but  it  never  did.  Steam  was  then 
introduced  in  place  of  extra  compressed  air  through  the 
same  pipes.  This  answered  the  purpose  admirably,  draining 
the  trenches  in  a  short  time.  It  afforded  an  ocular  demon- 
stration of  the  operation  of  a  Giffard  injector,  since  the  caisson 
simply  corresponds  to  the  interior  of  a  huge  boiler  and  steam 
under  the  same  tension  as  the  caisson  pressure  produced  the 
desired  result.  One  circumstance,  however,  led  to  its  early 
abandonment.  When  the  pump  had  worked  a  few  minutes, 
the  temperature  would  rise  to  a  hundred  degrees,  driving 
the  men  from  that  particular  chamber.  Recourse  was  then 
had  to  a  simple  flexible  suction  hose,  communicating  with  a 
pipe  leading  out  of  the  caisson.  The  end  of  this  hose  was 
held  in  the  water,  so  that  about  three-fourths  of  it  was  sub- 
merged. The  compressed  air  rushing  through  the  remain- 
der of  the  opening  kept  the  whole  column  of  water  in  motion 
at  a  rapid  rate.  This  mode  is,  of  course,  attended  with  a 
slight  loss  of  compressed  air,  but  it  proved  far  simpler  to 
raise  the  water  forty  feet  out  of  the  caisson  than  four  feet 
inside  of  the  caisson.  Soft  mud  and  fine  sand  passed  out 
readily  with  water. 

Boulders  under  the  Edge. 

The  occurrence  of  large  boulders  under  the  shoe  proved 
to  be  the  most  serious  obstacle  to  a  rapid  sinking  of  the  cais- 
son. As  long  as  the  water  trom  without  still  had  free  com- 
munication with  the  air  chamber,  they  had  to  be  attacked 
under  water,  the  most  tedious  part  of  the  operation  being 
the  removal  of  the  earth  in  which  they  were  imbedded. 
When  the  stones  extended  more  than  two  or  three  feet  out- 
side of  the  caisson,  no  attempt  was  made  to  haul  them  in, 
but  they  were  slowly  chipped  to  pieces,  until  enough  had 
been  removed  to  enable  the  edge  of  the  caisson  to  clear  them- 

As  soon  as  the  dredges  were  at  work,  the  excavated  mate- 
rial was  dumped  around  the  outside  of  the  caisson  with  a 
view  of  stopping  the  ready  passage  of  water  under  the  shoe. 
This  was  effected  after  a  time.  Then,  by  building  a  clay  dam 
around  the  boulder  on  the  inside,  and  filling  up  the  adjoining 


32 


space  with  bags,  it  became  possible  to  dig  a  comparatively 
dry  pit  underneath,  into  which  it  was  tumbled,  provided  it 
was  not  large. 

Several  boulders  occurred  which  delayed  all  settling  for 
three  or  four  days  at  a  time.  In  order  to  gain  time  a  special 
force  of  some  thirty  men  was  then  organized,  who  worked 
only  at  boulders  from  eleven  o'clock  at  night  until  six  A.M., 
when  the  regular  gangs  came  to  work. 

It  may  truly  be  said  that  the  results  of  the  first  month's  work 
were  not  very  encouraging.  We  had  a  material  to  deal  with 
which  is  difficult  to  remove,  even  under  favorable  circumstan- 
ces, on  top  of  the  ground.  The  rate  of  descent  had  not  aver- 
aged six  inches  per  week,  and  the  boulders  were  increasing 
instead  of  diminishing  in  numbers.  To  look  forward  to  a  rate 
of  lowering  of  even  one  foot  per  week  seemed  hopeless. 

The  work  inside  was  rendered  still  more  disagreeable  by 
the  frequent  "  blows,"  caused  by  the  rushing  out  of  the  com- 
pressed air  under  the  shoe.  This  would  continue  for  several 
minutes  until  a  returning  wave  of  inflowing  water  from  some 
other  part  of  the  caisson  would  check  it,  leaving,  however,  a 
foot  of  water  all  over  the  ground  for  some  time,  until  the  air 
pressure  drove  it  out  and  the  occurrence  repeated  itself. 
The  trenches  were  usually  flooded  thereby,  and  had  to  be 
pumped  or  bailed  out  incessantly.  These  flows  were  caused 
by  change  of  the  water  level  outside,  due  partly  to  passing 
steamboats,  but  principally  to  constant  changes  in  the 
tide.  The  thick  fog  which  accompanied  them  was  always 
an  indication  that  they  were  transpiring  in  some  part  of  the 
caisson, 

On  the  other  hand  we  were  gaining  daily  in  experience. 
The  workmen  became  more  accustomed  to  the  novel  situa- 
tion and  more  practiced  in  the  particular  kind  of  work  to  be 
done,  and  the  heaping  up  of  a  bank  of  earth  around  the  out- 
side, led  us  to  hope  that  when  the  caisson  had  sunk  a  few 
feet  lower,  the  conditions  of  air  pressure,  and  the  general 
regimen  oi  the  caisson  woidd  become  more  equable,  and, 
what  was  of  more  importance,  the  free  access  of  water  from 
without  would  probably  be  materially  curtailed.    These  ex- 


33 


pectations  were  more  than  realized.  In  a  short  time  water 
became  as  scarce  as  it  had  been'plenty  before. 

Blasting. 

When  the  caisson  had  arrived  at  the  depth  of  twenty-five 
feet  below  the  water-level,  the  boulders  became  so  large  and 
numerous  as  to  compel  us  at  last  to  resort  to  blasting. 

The  idea  of  using  powder  had  been  entertained  all  along, 
yet  our  imaginary  fears,  supported  by  plausible  reasoning, 
had  prevented  the  attempt  thus  far.  It  was  supposed  that 
the  effect  of  the  explosion  would  produce  a  violent  concus- 
sion in  that  dense  atmosphere,  rupturing  the  ear-drums  of 
the  men.  Again,  the  effect  upon  the  doors  and  valves  of  the 
air-locks  might  be  such  as  to  endanger  their  safety. 

The  principal  apprehensions  were,  however,  in  the  direc- 
tion of  the  water-shafts.  Here  were  two  columns  of  water 
seven  feet  square,  and  ultimately,  forty-five  feet  high,  held 
in  a  critical  balance  by  the  pressure  inside,  the  margin  of 
safety  being  an  immersion  of  less  than  two  feet  on  part  of 
the  lower  edge  of  the  shaft  in  the  pool  surrounding  it.  The 
sudden  explosion  might  rapidly  depress  the  level  of  the  pool 
and  allow  the  air  to  escape  underneath,  which  would  be  fatal 
both  to  the  caisson  as  well  as  the  men  inside.  Again,  as  re- 
gards blasting  under  the  shoe  and  partly  outside  of  it,  it  was 
feared  that  the  explosion  might  cause  a  vent  outward,  fol- 
lowed by  a  rush  of  air. 

The  result,  however,  justified  none  of  these  apprehensions. 

First,  a  trial  was  made  by  firing  a  pistol  with  successively 
heavier  charges,  then  small  charges  were  fired  off  by  a  fuse, 
and  soon  blasting  became  an  established  system.  The  good 
effects  were  at  once  apparent  in  the  lowering  of  the  caisson 
from  twelve  to  eighteen  inches  per  week  in  place  of  six 
inches.  As  many  as  twenty  blasts  were  fired  in  one  watch, 
the  men  merely  stepping  into  an  adjacent  chamber  to  escape 
the  flying  fragments.  The  hard  crystalline  trap  split  more 
easily  than  the  tough  gneiss  rock  or  rotten  quartz  boulder, 
The  trap  invariably  broke  into  three  nearly  equally-sized 
pieces. 


34 


THE   BROOKLYN  FOUNDATION. 


Great  care  had  to  be  exercised  in  guarding  against  setting 
fire  to  the  yellow  pine  roof  through  the  flash  and  the  burn- 
ing fuse.  The  gas  pipe  was  broken  several  times,  but  the 
flame  was  extinguished  before  damage  was  done.  In  blast- 
ing under  the  shoe  there  was  danger  of  injuring  it,  but 
nothing  serious  resulted.  In  fact  the  shoe  was  already  so 
badly  injured  as  to  amount  to  but  little.  The  armour-plates 
were  bent  and  crushed  and  parly  torn  off  by  jagged  points 
of  rocks,  the  inner  casting  was  cracked,  and  in  many  places 
the  whole  shoe  was  forced  in  ;  yet  no  air  escaped  because 
the  clay  was  tight  outside. 

One  convenient  way  of  disposing  of  boulders  under  the 
shoe,  was  to  drill  a  hole  through  them,  plant  the  charge  at 
the  bottom,  and  shoot  them  bodily  into  the  caisson,  where 
they  were  broken  up  at  leisure.  Boulders  were  found  four- 
teen feet  long  and  five  feet  in  diameter,  containing  three  hun- 
dred feet  and  more. 

The  powder  smoke  was  a  decided  nuisance.  It  would  fill 
the  chambers  for  half  an  hour  or  more  with  a  thick  cloud, 
obscuring  all  the  lights.  The  use  of  fine  rifle  powder  ame- 
liorated it  somewhat.  A  sprinkling  jet  of  water  to  throw  it 
down  mechanically  was  of  little  avail. 

The  sulphur  smell  was  not  disagreeable,  simply  because 
the  sense  of  smell  is  almost  entirely  lost  in  compressed  air. 
This  is  a  wise  provision  of  nature,  because  foul  odors  cer- 
tainly have  their  home  in  a  caisson. 

The  use  of  powder  has  proved  so  efficient  that  no  diffi- 
culty is  expected  in  leveling  off  the  irregular  surface  of 
gneiss  rock  upon  which  the  New  York  caisson  will  rest. 

In  order  to  expedite  the  laborious  task  of  hand  drilling,  a 
small  Burleigh  drill  was  procured,  mounted  on  a  tripod,  and 
capable  of  drilling  at  any  angle.  It  was  operated  by  com- 
pressed air  of  sixty  pounds  pressure,  and  worked  very  well. 
The  trouble,  however,  of  placing  it  in  position  and  moving 
it  from  chamber  to  chamber  more  than  counterbalanced  its 
other  advantages. 

As  the  caisson  descended  it  left  a  perpendicular  wall 
•  around  it,  the  soil  showing  but  little  signs  of  caving  in.  The 
side  moreover  having  an  inward  slope  of  one  in  ten  there 


3? 


was  constantly  an  open  cavity  between  the  caisson  and  this 
perpendicular  face  of  earth.  This  opening  in  some  places 
was  ten  feet  high  and  wide  enough  when  a  large  boulder  had 
been  removed  from  under  the  shoe  to  allow  a  man  to  go  en- 
tirely out  of  the  caisson.  Such  cases  tvere  rather  dangerous, 
since  on  two  occasions  the  air  had  a  chance  to  rush  out 
above  through  crevices  caused  by  slipping  of  earth.  Such 
escape  would  then  be  followed  by  cartloads  of  clay  and 
water,  pouring  in  underneath  the  shoe. 

The  Water  Shafts  and  Buckets. 

All  the  material  in  the  caisson  was  taken  out  through  the 
water  shaft  by  means  of  Morris  &  Cumming's  "  Grapnell 
bucket,"  an  instrument  which  is  analogous  to  the  human 
hand  in  its  action.  It  is  lowered  down  the  shaft  by  means 
of  two  ropes  in  an  open  position  ;  arrived  at  the  bottom  it 
closes  over  the  material,  filling  itself  at.  the  same  time.  It 
is  then  drawn  up  and  emptied  into  a  car  run  under  for  the 
purpose.  For  a  cut  and  description  I  would  refer  to  "  En- 
gineering "  p.  50  vol.  7.  Each  bucket  has  a  capacity  of 
one  and  a  half  yards,  a  lift  being  accomplished  every  four 
minutes.  The  estimated  efficiency,  making  all  due  allow- 
ances, was  eight  hundred  yards  per  day.  In  regular  harbor 
dredging  one  bucket  alone  will  raise  one  thousand  two  hun- 
dred yards  per  day. 

The  total  quantity  of  earth  removed  from  the  caisson  was 
over  20,000  yards.  Our  buckets  therefore  should  have  re- 
moved the  material  quite  comfortably  in  one  month's  time. 
In  place  of  one  month  five  were  required,  and  these  were 
five  months  of  incessant  toil  and  worry,  everlasting  breaking 
down  and  repairing,  and  constant  study  where  to  improve  if 
possible.  We  had  in  fact  a  material  which  could  not  be 
dredged.  The  Osgood  dredge  which  was  used  for  leveling 
off  before  the  caisson  was  floated  in,  could  accomplish  about 
ten  yards  a  day,  when  not  aided  by  submarine  blasting,  and 
the  Morris  &  Cummings  dredge  fished  all  day  without  bring- 
ing up  a  handful. 

The  first  disappointment  lay  in  the  fact  that  the  buckets 


i  36 


THE   BROOKLYN  FOUNDATION. 


would  not  make  their  own  hole  under  the  watershafts.  In 
all  other  parts  of  the  caisson  the  material  could  be  properly 
broken  up  and  prepared  for  the  dredges,  but  the  space  under 
the  shafts  was  inaccessible,  being  under  water  and  out  of 
sight.  1 

When  this  became  evident  there  was  but  one  course  left 
to  overcome  it.  This  consisted  in  bolting  a  wrought  iron 
cap  on  top  of  the  shaft  and  allowing  the  compressed  air  to 
rush  into  the  upper  part,  forcing  the  w  ater  column  down 
into  the  caisson  until  the  shaft  was  empty.  The  pool  below 
was  then  pumped  out,  As  fast  as  the  compressed  air  rushed 
into  the  shaft  a  quantity  of  stone  was  gradually  piled  up  on 
top  of  the  cap  to  prevent  it  from  being  blown  off. 

A  large  pit,  with  regular  sloping  sides,  from  six  to  eight 
feet  in  depth,  was  then  dug  out  under  the  shaft,  all  boulders 
being  lifted  out  and  removed.  This  pit  was  dug  in  the  dry, 
the  surface  river  water  being  kept  back  by  a  temporary  dam 
built  around  the  excavation.  The  dirt  as  it  is  dug  out  was 
wheeled  over  to  the  other  shaft.  When  the  pit  was  com- 
plete it  was  filled  with  water,  and  the  air  above  being  gra- 
dually allowed  to  escape,  the  water  would  rise  in  the  shaft 
until  the  column  of  balance  was  re-established.  The  stone 
and  caps  were  then  removed.  This  operation  was  per- 
formed c]uite  frequently.  Sometimes  the  shaft  would  run 
for  three  or  four  weeks  without  blowing  out,  then  again  only 
one  week ;  but  in  no  case  could  we  pass  below  the  point 
where  it  had  been  dug  out.  From  one  to  two  days  were 
always  lost  in  this  operation.  During  this  time  the  other 
shaft  did  all  the  work.  There  were  in  fact  so  many  repairs 
to  the  buckets  and  so  many  other  drawbacks  that  most  of 
the  time  only  one  shaft  was  running. 

The  action  of  the  bucket  when  it  dropped  on  the  material 
in  the  bottom  of  the  shaft  was  that  of  puddling  it  into  a  com- 
pact hard  pan,  harder  even  than  the  original  soil.  To  avoid 
this  it  was  necessary  for  four  men  to  be  constantly  stirring 
pool  to  keep  the  stuff  alive,  and  even  then  the  bottom  kept 
rising. 

A  mixture  of  stone  and  clay  was  sure  to  fill  up  the  hole  in 
a  few  hours.    The  stone,  moreover,  or  as  apt  to  become  so 


THE    BROOKLYN  FOUNDATION. 


firmly  imbedded  in  the  clay  that  the  teeth  of  the  bucket 
could  not  get  a  firm  hold,  it  therefore  became  a  necessity  at 
an  early  day  to  feed  all  the  stones  by  themselves  and  the  clay 
by  itself.  The  best  time  for  feeding  stone  was  when  the 
shaft  had  been  freshly  dug  out  and  they  were  allowed  to 
accumulate  until  then.  The  feeding  of  stone  required  much 
judgment.  The  bucket  could  easily  lift  out  any  stone  it 
could  catch  hold  of,  even  up  to  one  or  two  yards  in  size, 
provided  the  stone  was  shoved  into  the  right  position. 
Boulders  could  only  be  put  in  from  two  sides  of  the  shaft, 
and  one  stone  had  to  be  out  of  the  way  before  it  became  safe 
to  put  in  another.  The  shaft  being  rectangular  served  as  a 
guide  to  the  bucket,  compelling  it  to  come  down  in  the  same 
position  each  time ;  this  shape  was  a  great  advantage  in  one 
respect,  but  a  disadvantage  in  another,  because  the  square 
shaft  is  not  as  well  adapted  to  withstand  a  bursting  pressure 
during  the  operation  of  capping  without  a  dangerous  change 
of  form  which  had  to  be  met  by  external  bracing.  When- 
ever the  hole  under  the  shaft  was  pretty  well  filled  up,  the 
water  in  the  pool  was  allowed  to  sink  to  within  six  inches  of 
the  lower  edge,  and  attempts  were  made  to  cut  down  the 
puddled  material  with  steel  bars  and  sledges.  A  powerful 
stream  of  water  from  a  hose  was  found  useful  in  cutting  it 
away.  Often,  when  a  stone  got  into  a  wrong  position,  men 
would  dive  under  the  shaft  to  loosen  it.  When  the  lungs 
are  filled  with  compressed  air  a  person  can  remain  under 
water  from  three  to  four  minutes  with  ease. 

The  buckets  were  provided  with  heavy  teeth,  seven  inches 
long,  rivetted  fast  to  steel  cutting  edges,  six  by  one.  Many 
patterns  of  teeth  were  made  before  the  most  advantageous 
form  was  arrived  at.  A  tooth  which  answers  well  for  scoop- 
ing up  mud,  will  not  last  a  day  for  grappling  stones.  A 
supply  of  five  buckets  was  required  to  keep  two  in  working 
order.  The  buckets  very  rarely  became  directly  jammed  in 
the  shafts,  except  when^the  latter  had  been  freshly  dug  out, 
and  the  hole  below  was  deep  ;  the  buckets  were  then  apt  to 
catch  under  the  edge,  causing  vexatious  delays  at  times  ;  and 
unless  soon  removed,  they  would  then  be  imbedded  in  a 
deposit  of  clay  settling  down  from  the  water  in  the  shaft. 


38  THE   BROOKLYN  FOUNDATION. 


This  had  to  be  removed  by  a  hose  and  constant  bailing. 
When  the  shaft  was  forty-five  feet  high  the  water  in  it  held 
seven  feet  of  clay  in  suspension,  and  the  columns  of  water, 
in  place  of  being  forty-five  feet  high,  corresponding  to  a 
pressure  of  twenty  pounds  per  square  inch,  would  have  a 
height  of  only  thirty  feet,  showing  that  the  mixture  weighed 
some  ninety  pounds  per  cubic  foot  in  place  of  sixty-three 
pounds.  When  the  shaft  was  idle  for  a  short  time,  this 
mixture  would  settle  at  the  bottom  and  outside  of  it;  at  the 
same  time  the  lightened  water  column  would  rise,  requiring 
a  fresh  supply  below.  Constant  attention  was  required  not 
to  let  the  water  supply  get  too  low.  The  dredges  them- 
selves were  a  fruitful  source  of  water  waste.  When  they 
closed  tight,  which  was  seldom  the  case,  they  would  usually 
bring  up  two-thirds  water  and  one-third  mud,  the  water 
being  allowed  to  drain  through  openings  made  in  the  bucket. 
But  the  smallest  stone  coming  between  the  jaws,  or  any 
distortion  of  the  bucket  caused  by  dropping  it  down  on 
stones,  making  the  teeth  interfere,  would  prevent  their 
closing,  and  produce  a  considerable  washing  out  ot  the 
material,  as  the  bucket  was  drawn  up  through  the  water. 
This  was  the  principal  disadvantage  attending  their  use. 
And  yet,  with  all  our  drawbacks,  our  daily  experience  con- 
firmed us  in  the  assurance  that  we  had  selected  the  only 
instrument  capable  of  disposing  of  all  the  material  at  hand, 
no  matter  how  large  or  ill-shaped,  or  badly-packed  the 
boulder ;  no  matter  how  tenacious  the  clay  and  hardpan, 
nor  how  flowing  the  occasional  veins  of  quicksand. 

There  was,  indeed,  one  period  when  we  were  almost 
tempted  to  throw  the  buckets  overboard,  and  another 
method  was  devised  to  take  out  the  material.  This  consisted 
in  connecting  with  the  pit  under  the  water  shaft  a  wide  and 
deep  trench  leading  into  the  chamber.  In  the  bottom  of 
this  was  a  track  with  a  car  on  it,  arranged  with  ropes  for 
hauling  it  in  and  out  from  under  the  shaft.  On  this  car  was 
an  open  box  lowered  down  from  above,  when  the  car  was 
hauled  to  one  side  the  box  would  be  filled,  then  hauled  back 
and  hoisted,  the  hoisting  ropes  remaining  attached  to  it  all 
the  time.    This  whole  operation  would  have  to  take  place 


39 


under  water  and  out  of  sight.  The  plan  never  was  carried 
out.  It  might,  perhaps,  have  failed  from  the  covering  of 
the  track  by  sediment. 

Dumping  Cars. 

Two  kinds  of  dumping  cars  were  used.  One  style  being 
provided  with  a  turn-table  for  dumping  the  load  at  any 
point.  The  other  and  preferable  kind  dumped  on  rockers 
and  required  less  attendance. 

The  cars  were  hauled  back  and  forth  by  steam  power. 
Part  of  the  dirt  was  used  to  fill  a  vacant  slip  at  the  rear  of 
the  caisson.  The  bulk  of  the  stone  was  saved  and  used 
subsequently  for  filling  up  the  air  chamber.  The  remainder 
of  the  material  was  dumped  directly  into  the  river  and  re- 
dredged  by  an  Osgood  dredge,  this  plan  being  found 
cheaper  and  more  expeditious  than  direct  dumping  into 
boats.  The  cars  several  times  fell  into  the  shafts  but  were 
easily  picked  out  by  the  dredges. 

Management  of  Air  Pressure. 

Air  was  supplied  from  six  double  air  pumps,  located  three 
hundred  feet  from  caisson,  a  ten  inch  cast  iron  main  leading 
therefrom  ;  two  rubber  hose  of  six  inches  diameter  intro- 
duced it  directly  into  the  caisson.  When  any  lengthening 
out  of  the  shafts  had  to  be  done,  the  air  entered  only  by 
one  hose,  but  even  that  was  more  than  ample  in  size. 

At  the  beginning,  the  air  pressure  was  governed  entirely 
by  the  tides  and  regulated  itself  according  to  their  height. 
The  tightness  of  the  caisson  was  quite  satisfactory,  and  it 
was  soon  found  that  during  the  falling  of  the  tide  it  was 
practically  unnecessary  to  run  the  pumps  at  all,  the  loss  of 
head  counterbalancing  the  leakage.  But  with  a  rising  tide 
the  pumps  had  to  run  at  full  speed.  A  declining  pressure 
was  always  attended  by  thick  fogs  which  lasted  until  the 
tide  changed,  then,  the  caisson  would  remain  clear  for  the 
next  six  hours.  These  fogs  were  both  disagreeable  and 
detrimental  to  the  work  by  the  darkness  they  caused.  They 
could  at  times  be  partly  overcome  by  pumping  in  a  large 


40 


THE    KKOOK1.YN  FOUNDATION. 


excess  of  air,  but  not  always.  The  fog  would  occasionally 
be  confined  to  particular  chambers  while  others  would  be 
clear.  A  slight  blowing  off  under  the  shoe  always  caused 
a  fog  in  that  neighbourhood.  The  air  space  was  so  large, 
one  hundred  and  seventy  thousand  cubic  feet,  that  there 
was  considerable  latitude  for  variations  in  different  parts  of 
the  caisson.  Every  change  in  the  air  pressure  produced  a 
rise  or  fall  of  the  column  in  the  water  shaft.  As  the  tide 
fell,  the  water  filled  up  the  pool  under  the  shaft,  and,  running 
over  it,  would  endanger  the  safety  of  the  dam  surrounding 
it.  As  the  tide  rose  the  supply  in  the  pool  was  gradually 
exhausted  and  there  was  danger  of  the  air  blowing  out 
underneath  unless  supplied  artificially. 

As  soon  as  the  caisson  had  fairly  entered  into  the  water 
tight  and  air  tight  stratum  of  clay,  the  tides  no  longer  had 
an)-  effect  upon  the  air-pressure  whatever.  A  fixed  pressure 
was  maintained  according  to  the  calculated  head  of  water. 
The  clay  proved  so  tight  that  the  pressure  could  easily  be 
raised  from  four  to  five  pounds  higher  than  called  for  by  the 
head  of  water. 

This  satisfactory  state  continued  until  fresh  water  springs 
were  encountered.  Then  there  was  an  end  to  regularity  of 
air  pumping.  Sometimes  three  pumps  were  sufficient,  then 
again  all  six  pumps  running  at  their  maximum  speed,  could 
not  maintain  a  pressure  within  four  or  five  pounds  of  the 
standard,  and  as  the  pumps  were  overtaxed  they  broke 
down  and  the  pressure  ran  down  still  further.  A  judicious 
banking  up  of  the  shoe  below  with  clay  afforded  consider- 
able relief,  but  only  partial,  since  it  had  to  be  removed  again 
for  lowering  the  caisson.  We  thus  found  ourselves  in  the 
same  predicament  with  most  caisson-sinkers,  not  from 
leakage,  however,  but  from  want  of  water.  It  had  been 
supposed  that  a  pumping  capacity  of  four  hundred  cubic 
feet  per  minute,  would  prove  sufficient,  but  it  did  not. 

There  wras  one  critical  period  when  the  pressure  ran  down 
to  eleven  pounds  in  place  of  twenty,  where  it  should  have 
stood.  On  the  other  hand  when  the  caisson  had  reached  its 
depth  and  the  shoe  was  properly  banked  up,  four  pumps 
were  ample  to  keep  up  a  pressure  of  twenty  to  twenty-two 


THE    BROOKLYN  FOUNDATION. 


41 


pounds.  In  any  event  three  were  needed  to  supply  the 
necessary  fresh  air  for  one  hundred  and  twenty  men  and  the 
numerous  candles  and  gas  lights,  and  to  prevent  a  rise  in 
temperature.  The  thermometer  stood  uniformly  at  seventy- 
eight  degrees  day  and  night,  winter  and  summer,  whether 
the  temperature  outside  was  ninety  degrees  or  zero. 

Relation  of  Upward  Pressure  of  Air  to  Downward 
Pressure  of  Caisson. 

In  the  original  design  for  the  caisson,  it  was  the  intention 
to  make  the  air-chamber  one  vast  unbroken  space,  without 
dividing  or  supporting  frames  of  any  kind,  reliance  being 
placed  upon  the  solid  timber  platform  of  fifteen  feet  thick- 
ness to  transfer  all  strains  equally  from  the  shoe  inward.  To 
diminish  the  weight  above,  the  masonry  was  to  be  built  in- 
side of  a  wooden  cofferdam  placed  on  top  of  the  caisson. 

This  programme  was  quite  feasible  theoretically,  provided 
the  air  pressure  could  be  maintained  at  the  proper  standard 
without  possibility  of  failure,  and  provided  the  caisson  was 
sunk  through  a  soft  uniformly  yielding  material.  The  shoe 
and  sides  of  the  caisson  were  made  strong  enough  to  resist 
the  overweight  occurring  at  each  low  tide. 

The  requirements  of  launching,  however,  made  it  neces- 
sary to  introduce  five  heavy-trussed  frames  to  serve  as 
launching  frames  ;  they  divided  the  caisson  into  six  cham- 
bers, each  frame  being  also  well  braced  from  the  sides. 
These  frames  were  allowed  to  remain  in,  large  openings 
being  cut  in  them  for  passage  to  and  fro. 

Subsequent  events  proved  the  necessity  not  only  of  these 
frames,  but  of  double  the  additional  support. 

Very  little  attention  was  paid  to  the  matter  of  supports  at 
first ;  any  irregular  bearing  below  was  easily  distributed  by 
the  roof,  even  to  the  extent  of  having  entire  frames  unsup- 
ported at  times.  The  wooden  blocking  on  which  the  caisson 
was  supported  proved  sufficiently  elastic  to  yield  without 
crushing  to  any  extent. 

As  the  caisson  sank  deeper  much  of  the  dirt  coming  out 
was  dumped  on  top  of  it,  filling  up  all  spaces  not  occupied 


THE   BROOKLYN  FOUNDATION. 


by  masonry.  This  was  only  the  beginning  of  the  over- 
weight to  be  carried  ultimately.  Again,  at  very  low  tides, 
the  overweight  caused  by  them  was  equal  to  the  weight  of 
a  volume  of  water  one  hundred  and  sixty -eight,  by  one  hun- 
dred and  two,  by  seven  feet,  amounting  to  three  thousand 
seven  hundred  tons  alone. 

Blowing  Out  of  Water  Shaft. 

The  overweight  kept  slowly  increasing  until  one  Sunday 
morning  about  six  A.  M.,  the  south  water  shaft  blew  out 
every  particle  of  compressed  air,  leaving  the  caisson  in  an 
instant.  To  say  that  this  occurrence  was  an  accident  would 
certainly  be  wrong,  because  not  one  accident  in  a  hundred 
deserves  the  name.  In  this  case  it  was  simply  the  legiti- 
mate result  of  carelessness,  brought  about  by  an  over  confi- 
dence in  supposing  that  matters  would  take  care  of  them- 
selves. The  immediate  cause  of  the  blowing  out  lay  in  the 
washing  away  of  the  dam  around  the  pool  under  the  shaft. 
These  dams  washed  away  frequently  at  subsequent  periods, 
but  we  had  had  our  experience  and  our  lesson,  and  were 
prepared  for  it.  There  was  unfortunately  no  man  in  the 
caisson  at  the  time,  so  that  experience  is  lost.  Eye  wit- 
nesses outside  state  that  a  dense  column  of  water,  fog,  mud, 
and  stones  were  thrown  up  five  hundred  feet  into  the  air, 
accompanied  by  a  terrific  roar  and  a  shower  of  falling  frag- 
ments covering  the  houses  for  squares  around.  This  column 
was  seen  a  mile  off.  The  noise  was  so  frightful  that  the 
whole  neighborhood  was  stampeded  and  made  a  rush  up 
Fulton  street.  Even  the  toll  collectors  at  the  ferry  aban- 
doned their  tills.  There  were  three  men  on  the  caisson  at 
the  time  including  the  watchman.  He  reports  that  the  cur- 
rent of  air  rushing  toward  the  blowing  water  shaft  was  so 
strong  as  to  knock  him  down :  while  down  he  was  hit  on  the 
back  with  a  stone  and  further  than  that  he  does  not  remem- 
ber. One  of  the  other  men  jumped  into  the  river,  and  the 
third  buried  himself  in  a  coal  pile.  It  was  all  over  in  a  min- 
ute. Both  doors  of  the  air  lock  fell  open.  The  dry 
bottom  was  visible  through  the  air  and  water  shaft ;  not  a 


THE    BROOKLYN  FOUNDATION. 


43 


particle  of  water  had  entered  under  the  shoe  into  the  air- 
chamber  and  for  the  first  and  only  time  the  caison  could 
dispense  with  artificial  illumination.  As  soon  as  possible 
a  stream  of  water  was  passed  into  the  shafts  from  above,  the 
locks  were  closed  and  in  the  course  of  an  hour  the  pressure 
was  restored  to  fifteen  pounds,  corresponding  to  a  head  of 
thirty-one  feet. 

The  first  entry  into  the  caisson  was  made  with  consider- 
able misgiving,  but  none  of  our  fears  were  realized. 

The  total  settling  that  took  place  amouuted  to  ten  inches 
in  all.  Every  block  under  the  frames  and  posts  was  abso- 
lutely crushed,  the  ground  being  too  compact  to  yield  ;  none 
of  the  frames  however  were  injured  or  out  of  line.  The  brunt 
of  the  blow  was,  of  course,  taken  by  the  shoe  and  sides  of  the 
caisson.  One  sharp  boulder  in  number  two  chamber  had  cut 
the  armor  plate,  crushed  through  the  shoe  casting,  and  buried 
itself  a  foot  deep  into  the  heavy  oak  sill,  at  the  same  time 
forcing  in  the  sides  some  six  inches.  In  a  number  of  places 
the  sides  were  forced  in  to  that  amount,  but  in  no  instance 
were  they  forced  outward.  The  marvel  is  that  the  air  tight- 
ness was  not  impaired  in  the  least. 

The  nine  courses  of  timber  forming  the  sides  of  the  air 
chamber  were  permanently  compressed  to  the  extent  of  two 
inches,  as  was  shown  by  protruding  bolt-heads  and  the  shear- 
ing off  of  a  number  of  diagonal  bolts.  The  lower  sills  of  the 
frames  were  also  torn  where  the)7  came  upon  boulders. 

The  weight  of  the  caisson  at  the  time  was  seventeen  thou- 
sand, six  hundred  and  seventy-five  tons.  The  air  blew  out 
so  suddenly  that  this  weight  must  have  acted  with  consider- 
able impact  in  falling  through  the  space  of  ten  inches.  The 
bearing  surface  at  the  time  was  as  follows  ;  The  four  edges  of 
the  caisson  five  hundred  and  fifty  feet  long  and  seven  inches 
wide,  amounting  to  three  hundred  and  twenty-two  square 
feet ;  the  five  frames  each  one  hundred  feet  long  and  one 
foot  wide,  resting  on  twelve  blocks  one  foot  wide,  amounting 
to  sixty  square  feet,  and  giving  a  total  of  three  hundred  and 
eighty  two  square  feet  to  meet  the  above  pressure.  This  is 
at  the  rate  of  forty-six  tons  per  square  foot. 


44 


But  more  than  one-half  of  the  shoe  was  undermined  to  a 
depth  of  one  foot  or  more  which  reduced  the  practical  bear- 
ing substance  by  nearly  one  half.  At  the  commencement  of 
the  shock,  there  was  therefore  a  pressure  of  eighty  tons  per 
square  foot,  no  allowance  being  made  lor  impact,  which  may 
have  doubled  this  rate.  The  caisson  had  settled  ten  inches. 
The  shoe  had  buried  itself  so  as  to  present  a  width  of  twelve 
inches  and  through  the  crushing  of  the  blocks  the  frames 
were  in  many  places  resting  bodily  on  the  ground.  The 
settling  had  therefore  stopped  when  a  bearing  surface  of 
seven  hundred  and  seventy-five  square  feet  had  been  reached 
giving  a  pressure  of  twenty-three  tons  per  square  foot. 

The  ultimate  pressure  on  the  base  of  the  caisson  due  to 
the  weight  of  the  tower  and  superstructure  will  be  only  five 
tons  per  square  foot  ;  hence  the  margin  of  safety  against 
crushing  is  ample.  All  the  above  extreme  rates  of  trans- 
verse crushing  are  within  the  limits  of  good  yellow  pine. 
The  fact  that  the  majority  of  the  blocks  did  crush  is  attribu- 
table mainly  to  their  irregular  bearing  and  to  their  short- 
ness, a  block  of  four  feet  in  length  will  bear  a  much  larger 
pressure  upon  one  square  foot  of  its  surface  than  a  block  of 
two  feet  in  length  ;  the  same  is  true  in  regard  to  relative 
breadth.  Yellow  pine  is  essentially  a  heart  wood,  and  before 
yielding  to  compression  it  will  split  out  side  ways  awav 
from  the  heart.  In  the  root  of  the  caisson  no  effects  whatever 
were  produced  by  the  pressure  of  posts.  The  timbers  are 
bolted  so  close  laterlly  that  no  yeilding  sideways  can  take 
place.  Subsequent  examinations  showed  that  the  roof  of  the 
air-chamber  has  assumed  a  permanent  average  depression  of 
four  and  one-half  inches,  being  least  in  the  end  chamber,  and 
greatest  near  the  water  shafts,  where  there  was  the  least 
support  by  frames,  and  where  these  openings  had  cut  the 
timber  through  from  top  to  bottom.  This  deflection  never 
increased  any.  The  amount  is  comparatively  small  when  we 
consider  that  the  transverse  span  is  one  hundred  and  two 
feet  between  bearings,  that  the  whole  caisson  and  timber 
above  it  is  a  composite  structure,  bolted  together,  and  that 
the  joints  in  the  timber  are  butt  joints.    That  amount  of 


THE    BROOKLYN  FOUNDATION'.  45 


deflection  is  scarcely  sufficient  to  bring;  all  the  bolts  to  a  full 

J  O 

bearing. 

Additional  Shores. 

As  the  caisson  proceeded  in  its  downward  course,  the  dis- 
proportion between  the  dead  weight  above  and  the  air  pres- 
sure from  below  became  greater  and  greater.  For  instance, 
on  the  15th  of  November,  the  escape  of  air  under  the  shoe 
was  so  strong  that  no  more  than  ten  pounds  of  air  pressure 
could  be  maintained.  The  over-pressure  entailed  thereby 
was  twelve  thousand  two  hundred  and  forty  tons.  This  was 
received  by  a  bearing  surface  of  two  hundred  and  eighty 
square  feet,  causing  a  pressure  of  forty-four  tons  per  square 
foot. 

In  order  to  meet  this  constantly  increasing  over-weight  a 
large  number  of  additional  shores  were  introduced  into  the 
caisson.  They  rested  upon  a  block  and  wedges,  and  sup- 
ported a  cap  spiked  against  the  roof.  The  presence  of  these 
shores  added  considerable  to  the  labor  of  lowering  the  cais- 
son, and  diminished  the  available  working  space  otherwise. 
They  gave,  however,  a  positive  assurance  against  any  crush- 
ing weight  from  above,  and  could  moreover  be  easily  re- 
moved when  a  boulder  was  taken  out,  which  could  not  be 
done  with  the  permanent  frames. 

The  downward  movement  of  the  caisson  was  usually  so 
impulsive  that  the  blocks  under  the  posts  were  allowed  to 
crush  and  were  subsequently  dug  out.  In  fact,  their  crush- 
ing was  the  only  indication  we  had  that  any  portion  of  the 
caisson  was  bearing  particularly  hard.  The  noise  made  by 
splitting  of  blocks  and  posts  was  rather  ominous,  and  inclined 
to  make  the  reflecting  mind  nervous  in  view  of  the  impend- 
ing mass  of  thirty  thousand  tons  overhead. 

Side  Friction. 
No  satisfactory  estimate  could  ever  be  made  of  side  fric- 
tion. There  must  have  been  some,  but  of  a  very  irregular  char- 
acter. At  times  an  outside  boulder  would  apparently  hold  one 
end  of  the  caisson  until  a  bolt  head  or  part  of  the  timber 
gave  way.    The  batter  on  the  outside  being  one  fool  in  ten. 


46 


THE   BROOKLYN  FOUNDATION. 


was  calculated  to  relieve  the  caisson  from  side  friction.  The 
workmen,  however,  never  dug  out  far  enough  behind  the 
shoe,  thus  causing  great  friction  for  several  feet  up  the  sides, 
and  pressing  in  the  sides  to  as  much  as  nine  inches  in  some 
places.  The  side  friction  probably  never  exceeded  three 
thousand  tons.  The  larger  the  base  of  a  caisson  the  smaller 
is  the  percentage  of  side  friction  available  to  counteract  down- 
ward pressure,  whereas  in  a  narrow  caisson,  penetrating  a 
uniform  sand,  it  is  often  sufficient  to  counterbalance  the  whole 
weight. 

Bkick  Piers. 

When  the  caisson  had  arrived  within  three  feet  of  its 
proposed  resting  place,  it  was  considered  advisable  while 
the  air  chamber  was  being  filled  with  concrete,  to  erect  for 
its  support  seventy-two  brick  piers,  systematically  located, 
and  averaging  twenty  square  feet  of  base.  Their  ultimate 
capacity  was  just  sufficient  to  support  the  whole  weight 
above  in  case  the  air  should  blow  out.  It  was  felt  that 
where  openings  exist  like  the  water  shafts  or  supply  shafts, 
there  exists  also  a  possibility  of  the  air  blowing  out,  no 
matter  what  precautions  are  taken,  or  how  much  care  is 
used.  The  precaution  was,  therefore,  safe,  even  if  not 
needed.  Subsequent  events  showed  the  necessity  of  it. 
The  piers  were  completed  in  three  weeks,  requiring  250,000 
bricks  in  their  construction.  The  inevitable  strike  attended 
the  employment  of  the  large  force  of  bricklayers,  men  new 
to  the  place  and  circumstances.  It  was  easily  overcome, 
however,  and  caused  no  delay. 

Blowing  Out  of  Supply  Shaft. 

Shortly  after  the  caisson  had  come  to  a  bearing  on  the 
piers  and  the  concreting  had  been  in  process  a  fortnight, 
one  of  the  supply  shafts  blew  out.  The  tension  of  the  air 
was  reduced  in  a  few  minutes  from  eighteen  to  four  pounds, 
and  the  piers  had  to  bear  the  brunt  of  the  weight. 

A  few  words  will  suffice  to  explain  the  mode  of  operating 
the  supply  shaft.    It  consists  of  a  tube  forty-five  feet  long 


THE    BROOKLYN  FOUNDATION. 


47 


and  twenty-one  inches  diameter,  inside,  with  the  door  at  the 
bottom  opening  into  the  air-chamber,  and  a  long  door  on 
top,  through  which  the  material  is  thrown  in.    When  the 
upper  door  is  open,  the  lower  one  is  held  shut  by  the  air- 
pressure,  assisted  by  two  iron  clamps  worked  by  levers.  As 
soon  as  a  certain  quantity  of  material  has  been  thrown  in, 
the  upper  door  is  pulled  up,  and  the  compressed  air  being 
then  allowed  to  enter,  firmly  closes  it.    When  the  shaft  is 
filled  with  compressed  air,  a  signal  is  given  to  the  attendant 
below,  who  removes  the  lugs,  the  door  falls,  and  the  con- 
tents of  the  shaft  drop  into  the  air  chamber.    The  operation 
is  very  simple  and  rapid,  and  perfectly  safe  with  the  most 
ordinary  precaution.    Two  of  these  shafts  were  found  ample 
to  furnish  all  the  material  required  for  filling  vip  the  caisson. 
They  had  worked  well  for  five  weeks,  but  danger  always 
steps  in,   when  through  daily   use  and  familiarity  the  at- 
tendants become  careless  and  reckless.    It  had  occurred  at 
times  that  a  charge  of  building  stones  or  brick  would 
become  jammed,  and  only  part  of  a  load  would  drop  out. 
To  ascertain  this  fact,  a  string  with  a  weight  was  let  down 
from  above  each  time,  so  as  to  avoid  putting  in  a  double 
charge.    Upon  this  occasion  a  charge  had  jammed  ;  the  men 
clumped  in  another  without  measuring  the  depth  either 
before  or  after,  and  then  gave  the  signal  to  the  man  below, 
without  shutting  the  upper  door,  or  letting  on  the  com- 
pressed air.    The  second  charge  happened  to  loosen  the  first, 
and  the  two  together  overcame  the  pressure  against  the 
lower  door,  when  the  lugs  were  turned.    As  soon  as  this 
happened,  the  air  commenced  to  rush  out  of  the  caisson  with 
a  great  noise,  carrying  up  stone  and  gravel  with  it.  The 
men  above  ran  away,  leaving  those  below  to  their  fate.  Any 
one  with  the  least  presence  of  mind  could  have  closed  the 
upper  door  by  simply  pulling  at  the  rope. 

I  happened  to  be  on  the  caisson  at  the  time.  The  noise 
was  so  deafening  that  no  voice  could  be  heard.  The  setting 
free  of  water  vapor  from  the  rarifying  air,  producing  a  dark, 
impenetrable  cloud  of  mist,  and  extinguished  the  lights.  No 
man  knew  where  he  was  going,  all  ran  against  pillars  or 


48 


posts,  or  fell  over  each  other  in  the  darkness.    The  water 
rose  to  our  knees,  and  we  supposed,  of  course  that  the  river 
had  broken  in.    It  was  afterward  ascertained  that  this  was 
due  to  the  sudden  discharge  of  the  columns  of  water  con- 
tained in  the  water  shafts.     I   was  in  a  remote  part  of 
the  caisson  at   the  ,  time  ;  half  a  minute  elapsed  before  I 
realized  what   was  occurring,  and  had  groped  my  way 
to   the   supply    shaft    where   the   air   was  blowing  out. 
Here    I   joined    several    firemen    in   scraping   away  the 
heaps  of  gravel  and  large  stones  lying  under  the  shaft,  which 
prevented  the  lower  door  from  being  closed.    The  size  of 
this  heap  proved  the  fact  of  the  double  charge.      From  two 
to  three  minutes  elapsed  before  we  succeeded  in  closing  the 
lower  doors.     Of  course  everything  was  all  over  then,  and 
the  pressure,  which  had  run  down  from  seventeen  to  four 
pounds,  was  fully  restored  in  the  course  of  fifteen  minutes. 
A  clear  and  pure  atmosphere  accompanied  it.     The  effect 
upon  the  human  system,  and  the  ears,  was  slight,  no  more 
than  is  experienced  in  passing  out  of  the  airlock. 

Careful  examination  was  made  to  see  what  effect  the  weight 
of  thirty  thousand  tons  had  upon  the  brick  pillars  and  other 
supports.  Although  the  pressure  on  the  piers  was  twelve 
tons  per  square  foot,  these  showed  no  signs  of  yielding.  In 
the  neighborhood  of  the  water  shafts  and  supply  shafts,  where 
there  were  no  brick  piers  or  other  supports,  a  slight  local 
depression  took  place  in  the  roof.  The  occurrence  demon- 
strated the  fact  that  the  pillars  were  strong  enough  to  bear 
the  whole  load,  and  also  proved  the  necessity  of  their  erec- 
tion. A  few  small  springs  of  brackish  and  fresh  water  started 
beneath  the  concrete  under  the  shoe,  but  was  easily  repress- 
ed.   There  was  no  increase  ot  air  leakage. 

It  was  rather  remarkable  to  notice  that  there  was  no  rush 
of  air  in  the  immediate  vicinity  of  the  supply  shaft,  not  even 
for  several  feet  up  the  shaft  ;  the  action  was  one  of  free  ex- 
pansion in  all  directions. 

The  question  naturally  arises,  what  would  have  been  the 
result  if  water  had  entered  the  caisson  as  rapidlv  as  the  air 
escaped.    The  experience  here  showed  that  the  confusion 


THE    BROOKLYN  FOUNDATION. 


the  darkness,  and  other  obstacles  were  sufficient  to  prevent 
the  majority  of  the  men  from  making  their  escape  by  the 
airlocks,  no  matter  how  ample  the  facilities.  If  the  water 
entered  as  rapidly  as  the  air  escaped  there  would  then  be 
the  same  pressure  of  air  during  the  whole  time  of  escape. 
Now  it  so  happens  that  the  supply  shafts  project  two  feet 
below  the  roof  into  the  air-chamber ;  as  soon,  therefore,  as 
the  water  reaches  the  bottom  of  the  shaft  it  will  instantly 
rise  in  it,  forming  a  column  of  balance  and  checking  the  fur- 
ther escape  of  air.  The  remaining  two  feet  would  form  a 
breathing  space  sufficient  for  the  men  to  live,  and  even  if  the 
rush  of  water  were  to  reduce  this  space  to  one  foot,  there 
would  be  enough  left  to  save  all  hands  who  retained  sufficient 
presence  of  mind. 

Filling  up  the  Air-Chamber. 

The  operation  of  the  two  supply  shafts  has  already  been 
described.  Their  capacity  proved  ample  for  all  require- 
ments. Concrete  was  laid  at  the  rate  of  one  hundred  yards 
per  day  of  sixteen  hours.  As  the  space  became  more  con- 
tracted, this  quantity  was  reduced.  A  great  saving  in  time 
as  well  as  amount  of  concrete  was  effected  by  letting  the 
edges  of  the  caisson  sink  into  the  ground  three  and  a  half 
feet  deeper  than  the  average  level  of  the  bottom.  This  re- 
duced the  height  of  the  air  chamber  from  nine  feet  six  inches 
to  six  feet,  and  diminished  the  amount  to  be  filled  in  about 
one-third. 

The  concrete  consisted  of  one  part  of  Rosendale  cement, 
two  of  sand,  and  four  of  small-sized  gravel.  The  sand  and 
cement  were  mixed  above  and  passed  through  one  shaft,  the 
gravel  through  the  other.  The  gravel  came  from  the  Long 
Island  beaches,  where  the  action  of  the  waves  had  washed  it 
absolutely  clean,  and  sorted  it  in  layers  of  uniform  size.  Dur- 
ing most  of  the  time  the  weather  outside  was  so  cold  that 
the  concrete  had  to  be  mixed  below.  At  a  later  period  it 
was  mixed  above  and  sent  down  directly.  No  trouble  was 
ever  experienced  from  its  setting  before  it  was  spread  out  and 
rammed,  nor  did  it  ever  set  in  the  supply  shafts  ;  much  labor 
can  be  saved  thereby  in  the  air-chamber.    The  gravel  being 


5o 


Tin;  ukooKi.YN  ro i  n dai ion. 


full  of  frost,  frequently  froze  hist  in  the  shafts;  this  was 
obviated  by  introducing  a  steam  pipe  and  thawing  out  each 
charge. 

The  boulders  which  had  been  taken  out  oi  the  caisson  were 
broken  up  into  square  blocks,  and  again  built  in  below  with 
the  concrete.  The  general  mode  pursued  in  the  filling  was, 
to  build  narrow  bulkheads  from  three  to  four  feet  wide  from 
the  floor  to  the  roof  all  around.  The  sides  being  kept  ver- 
tical by  boards,  which  were  removed  after  concrete  had 
hardened.  Next  to  the  roof  a  shallow,  sloping  layer  was 
rammed  in  with  narrow,  flat-faced  iron  rammers.  This  place 
required  careful  watching  as  it  was  apt  to  be  slighted,  and 
yet  was  the  most  important  point  in  all  the  filling.  When, 
in  making  the  repairs  of  the  fire,  it  became  necessary  to  cut 
out  a  considerable  portion  of  the  concrete,  it  was  found  that 
the  part  next  to  the  roof  was  the  most  compact  portion  of 
the  whole.  Every  layer  of  concrete  was  allowed  to  remain 
for  five  hours  before  another  was  put  on.  The  total  quantity 
required  was  about  four  thousand  yards  including  the  brick 
piers. 

The  rapid  influx  of  fresh  water  springs  prevented  any  ma- 
terial reduction  of  the  air  pressure.  The  water-shafts  were 
cut  away  below  and  filled  up  with  concrete,  to  the  line  of  the 
roof.  After  the  cavity  was  filled,  and  the  air  pressure  taken 
off,  it  was  found  that  sufficient  wat  er  leaked  through  the  con- 
crete to  fill  the  shafts  to  the  top.  They  were  then  filled  from  # 
above  with  concrete,  lowered  down  in  self-dumping  buckets. 
The  caps  to  these  shafts  should  have  been  provided  with 
small  air-locks,  so  as  to  fill  them  in  the  dry.  The  water  ris- 
ing in  these  shafts  was  perfectly  fresh,  without  a  trace  of  salt, 
which  shows  that  the  timbers  will  be  saturated  with  fresh 
water.  Its  temperature  was  remarkably  high,  seventy  de- 
grees, whereas,  that  of  pure  spring  water  is  fifty-five  degrees, 
and  of  the  river,  fifty  degrees.  This  would  indicate  that  the 
whole  mass  of  timber  and  concrete  must  have  been  heated  to 
the  temperature  existing  in  the  air-chamber,  which  averaged 
from  seventy  to  eighty  degrees  throughout  the  winter,  and 
was  even  greater  up  in  the  timber,  where  all  the  hot  air  was 


THE    BROOKLYN"  FOUNDATION. 


51 


concentrated.  It  is  also  probable  that  the  water  penetrating 
the  concrete  as  soon  as  the  air-pressure  ceased,  would  pro- 
duce some  heat  by  contact  with  the  small  quantity  of  free  lime 
there  existing.  The  concrete  filling  was  permeated  by  air 
throughout.  Even-  when  the  last  charge  was  put  in  the  air 
bubbled  up  under  the  edges  of  the  caisson,  requiring  a  pas- 
sage of  fifty  feet  through  the  concrete. 

Fires. 

The  danger  from  fire  in  an  atmosphere  of  compressed  air 
is  very  serious,  and  becomes  doubly  so,  with  a  wooden 
caisson  penetrating  a  water  tight  stratum.    Already  at  a 
pressure  of  twenty-five  pounds  per  square  inch,  the  flame  of 
a  candle  will  return  when  blown  out,  and  all  inflammable 
materials  have  to  be  carefully  banished.    Several  minor  fires 
at  the  beginning  showed  the  necessity  ol  caution.    One  was 
of  sufficient  magnitude  to  demand  the  flooding  of  the  cais- 
son, which  was  then  easily  accomplished,  because  the  water 
entered  freely  under  the  shoe,  as  the  air  escaped  through 
valves  provided  for  that  purpose.    When  therefore  the  fact 
was  settled  that  the  river  water  was  permanently  excluded 
from  the  caisson,  it  became  a  matter  of  primary  importance 
to  guard  against  fires,  and  accordingly  two  hose  connections 
were  provided,  throwing  streams  of  one  and  a  half  inches  at 
sixty-five  pounds  pressure.    Steam  pipes  were  introduced, 
connecting  with  boilers  outside.    In  addition  all  seams  be- 
tween the  roof  timbers  were  carefully  pointed  with  cement, 
and  iron  shields  provided  over  the  permanent  lights.  It 
was  made  the  special  duty  of  two  men  to  watch  continually 
over  all  lights.    Notwithstanding  all  these  precautions  there 
was  a  seam  where  the  supporting  frames  join  the  roof  that 
had  not  been  pointed ;   an  empty  candle  box  was  nailed 
under  it,  in  which  some  man  kept  his  dinner,  and  while 
getting  it  he  probably  held  a  candle  against  the  roof  for 
some  time.    This  proved  to  be  the  heel  of  Achilles,   a  fire 
being  discovered  there  on  the  evening  of  December  2. 
Being  directly  over  the  frame  it  had  remained  undiscov- 
ered, until  the  latter  had  been  partially  burnt  through. 
From  its  size  it  is  supposed  to  have  been  burning  for  several 


52 


THK    BROOKLYN  FOUNDATION. 


hours  previous.  A  slight  stampede  ensued  among  the  men, 
but  no  one  left  the  caisson.  All  appliances  for  putting  it 
out  were  brought  to  bear.  While  the  hose  was  getting 
ready,  two  large  cylinders  of  carbonic  acid  gas  under  two 
hundred  and  twenty-five  pounds  pressure  were  discharged 
into  it  without  producing  any  effect  whatever.  As  soon  as 
the  stream  was  stopped  the  timber  would  reignite  immedi- 
ately. The  two  streams  of  water,  however,  soon  extin- 
guished all  fire  that  could  be  seen  at  the  time.  There  was 
a  violent  draft  of  air  through  the  burnt  aperture.  This  was 
stopped  with  cement,  and  the  two  streams  of  water  were 
allowed  to  play  in  the  hole  for  two  hours.  At  the  end  of 
that  time  one  of  them  was  replaced  by  steam  at  ninety 
pounds  pressure,  and  allowed  to  run  for  half  an  hour.  It 
was  impossible  to  ascertain  whether  the  steam  was  of  any 
benefit.  It  was,  therefore,  shortly  stopped  off  and  the  water 
turned  on  again.    The  steam  may  even  have  aided  the  draft. 

In  the  meantime  the  question  of  flooding  the  caisson  was 
seriously  discussed.  To  extinguish  the  fire  without  having 
recourse  to  this  resort  was  very  desirable,  yet,  on  the  other 
hand,  if  the  fire  was  not  out,  it  was  simply  a  question  of 
time  how  soon  the  entire  structure  would  be  destroyed. 

One  great  objection  to  the  flooding  was  the  condition  of 
the  water  shaft,  which  was  capped  above  and  resting  below 
on  some  boulders.  A  gang  of  men  were  busy  all  night 
digging  them  out.  The  flooding  would  necessarily  be  ac- 
companied by  some  settling  of  the  caisson  since  it  was? 
equivalent  to  an  extra  weight  of  twenty-eight  thousand 
tons,  and  if  the  water  shaft  came  down  on  the  boulders  it 
might  become  so  crippled  as  to  impair  the  tightness  of  the 
caisson  permanently. 

The  problem  to  be  asked  in  the  flooding  was  to  substitute 
the  compressed  air  by  the  water  poured  in  through  the 
water  shafts  from  above,  and  to  so  regulate  the  escape  of 
the  air  as  to  always  maintain  the  same  pressure  against  the 
roof  of  the  caisson,  even  up  to  the  last  inch  below  the  roof, 
until  the  water  had  entirely  replaced  the  air.  The  supply 
of  the  former  would  of  course  be  limited  and  variable,  and 
if  the  air  should  be  all  out  before  the  water  had  reached  the 


THE    BROOKLYN  FOUNDATION.  53 


roof,  the  result  would  be  a  sudden  drop  of  the  caisson,  and 
the  destruction  of  all  supports  by  the  weight  of  twenty- 
eight  thousand  tons,  besides  running  the  risk  of  causing  the 
caisson  to  leak  so  badly  as  to  render  its  reinflation  im- 
possible. The  situation  was  entirely  different  from  that  at 
the  first  fire,  when  the  water  rushed  in  under  the  edges  as 
rapidly  as  the  air  escaped,  and  thus  maintained  a  uniform 
pressure  at  all  times.  These  various  considerations  un- 
fortunately appeared  of  great  weight  at  that  time  and  under 
such  circumstances  of  mental  excitement  and  bodily  pros- 
tration. It  was  concluded  first  to  exhaust  all  other  means 
for  ascertaining  whether  the  fire  was  out.  This  resolve  was 
strengthened  by  the  fact  that  at  four  A.  M.  the  water  thrown 
by  the  hose  ran  back  through  the  orifice  into  which  it  was 
thrown,  therebv  leading  us  to  think  that  the  burnt  cavity 
was  filled  with  water  and  could  hold  no  more. 

The  only  way  to  ascertain  the  presence  of  fire  was  to 
bore  for  it  at  random  through  the  solid  timbers.  A  number 
of  holes  were  bored  up  for  a  distance  of  two  feet.  They 
showed  no  fire.  Others  were  then  bored  up  for  three  feet, 
showing  no  fire.  This  result  was  of  course  encouraging. 
Time  was  lost  in  lengthening  out  augers  and  also  in  the 
boring,  because  the  draft  carried  the  chips  up.  At  eight 
A.  M.  a  hole  four  feet  high  revealed  the  dreaded  fact  that  the 
fourth  course  of  timber  was  one  mass  of  living  coals. 

All  available  engines  of  the  Fire  Department  were  soon  at 
work  pouring  water  into  the  other  water  shaft.  Additional 
forces  were  brought  up  by  and  by.  The  Fuller,  a  harbor 
fire  boat,  supplied  eight  powerful  streams;  the  J.  L.  Tebo 
three,  and  the  navy  yard  tug  two  more.  By  10  A.  M.,  thirty- 
eight  streams  of  water  were  flowing  into  the  caisson,  beside 
the  water  from  the  pipes  in  the  caisson  itself. 

Our  water-shafts  most  certainly  proved  their  value  in  this 
instance.  Without  them  the  introduction  of  such  a  quantity 
of  water  in  so  short  a  time  would  have  been  out  of  the  ques- 
tion. By  half-past  three  p.  m.  the  air-chamber  was  filled. 
Total  quantity  of  water  required,  one  million  three  hundred 
and  fifty  thousand  gallons. 

The  escape  of  air  was  regulated  by  the  pressure  gauges  ; 


54 


THE    HKOOKLYN  FOUNDATION. 


at  times,  as  it  escaped  too  rapidly,  the  pumps  were  started 
to  restore  the  pressure.  When  the  water  had  reached  within 
two  feet  of  the  roof,  the  escape  of  air  through  the  large 
valves  was  thereby  cut  off,  and  the  balance  escaped  by  leak- 
age and  through  two  small  one  and  one-half  inch  pipes, 
reaching  within  a  half-inch  of  the  roof.  During  the  latter 
stage  the  pressure  fell  at  one  time  from  nineteen  to  ten 
pounds.  The  settling  of  the  caisson  of  two  inches  was  prob- 
ably due  to  that.  After  the  flooding,  the  water  in  the  shafts 
was  kept  ten  feet  above  tide  level,  and  remained  so  with 
very  little  feeding,  thus  showing  that  the  earth  was  practic- 
ally water-tight  under  the  shoe. 

The  caisson  remained  flooded  for  two  and  one-half  days. 
Six  hours  were  required  to  force  out  the  water  again.  It  all 
ran  out  over  the  top  of  the  water-shafts,  requiring  about 
twenty-two  pounds  of  air  pressure. 

The  structure  proved  tighter  than  before  the  flooding, 
owing  to  the  swelling  of  the  timber.  An  inspection  below 
showed  but  little  apparent  damage,  beyond  blocks  that  were 
crushed  and  some  posts  thrown  over. 

The  building  of  the  brick  piers  was  at  once  resumed  and 
completed  in  two  weeks,  and  the  caisson  lowered  down  on 
them  through  the  remaining  distance  of  two  feet. 

For  several  weeks  subsequently  the  odor  of  turpentine 
and  other  products  of  the  combustion  of  yellow  pine  was 
very  strong  above  the  caisson,  being  forced  out  with  the  air 
bubbles.  They  gave  rise  to # very  unpleasant  suspicions, 
which  were  happily  dissipated  by  time. 

A  large  quantity  of  frothy  pyrolignic  acid  also  made  its 
appearance  on  top  of  the  masonry,  showing  that  a  des- 
tructive distillation  of  wood  had  been  going  on.  This  con- 
tinued for  over  three  months,  as  long  as  any  air  remained 
below. 

Extent  of  Fire,  and  Repairs. 

About  two  hundred  borings  were  made  in  the  roof  of  the 
caisson  for  the  purpose  of  ascertaining  the  extent  of  the  fire, 
both  laterally  as  well  as  vertically.  It  was  found  that  it  was 
confined  to  the  third  and  fourth  courses  of  timber,  but  had 


55 


spread  out  laterally  in  many  different  directions,  covering  a 
much  larger  area  than  was  anticipated,  the  remotest  points 
being  some  fifty  feet  apart.  The  fact  of  the  air  rushing  out 
through  every  bore  hole  seemed  to  show  that  we  had  to  de- 
pend upon  the  immediate  roof  for  retaining  the  compressed 
air.  Hence  the  first  conclusion  arrived  at  in  regard  to 
making  the  repairs  was  to  wait  until  the  air-chamber  had 
been  partly  filled  in  around  the  edges,  then  let  off  the  air 
pressure  entirely,  trusting  to  the  pillars  and  concrete  to 
support  the  weight,  and  whatever  spring  water  came  in  was 
to  be  pumped  out.  Large  holes  could  then  be  cut  in  the 
roof  and  the  repairs  made,  provided  that  the  waters  did  not 
come  in  too  fast  through  the  timbers.  It  was  very  desir- 
able, however,  to  gain  time  and  do  as  much  as  possible  at 
once,  while  the  air-pressure  was  yet  on.  This  made  it 
necessary  to  check  in  some  way  the  loss  of  air  attending  the 
cutting  away  of  the  timber. 

With  this  object  in  view  it  appeared  advisable  to  inject 
cement  into  the  burnt  cavities  through  the  bore  holes  until 
the  leakage  was  stopped.  Accordingly  a  cylinder  was  pre- 
pared with  a  piston  and  a  one  and  a  quarter  inch  injecting 
pipe,  and  when  freshly  filled  was  placed  under  a  hole,  and 
the  cement  forced  up  by  a  screw  jack.  This  worked  well. 
Experiments  showed  that  a  mixture  of  one  part  of  cement 
and  one  of  sand  could  be  forced  a  distance  of  ten  feet 
through  a  small  pipe  and  then  would  spread  out  laterally  to 
some  distance.  As  soon,  however,  as  a  certain  moderate 
amount  of  resistance  was  experienced,  all  the  water  would 
be  squeezed  out,  and  it  became  impossible  to  force  the 
charge  another  inch.  We  soon  found  that  the  mere  suction 
of  air  through  the  blow  holes  was  sufficient,  to  draw  up  the 
cement  loosely  through  a  pipe.  When  a  hole  was  clogged 
the  stuffer  was  applied  to  compact  it.  By  these  means  six 
hundred  cubic  feet  of  cement  were  injected,  and  all  escape 
of  air  ceased.  A  number  of  trial  bore  holes  failed  to  dis- 
close any  space  not  filled  with  hard  cement.  We  alread}' 
flattered  ourselves  that  this  filling  might  answer  every  pur- 
pose, but  in  order  to  make  sure,  one  large  hole,  six  feet 


56 


THE   BROOKLYN  FOUNDATION. 


square,  was  cut  up  into  the  roof  through  a  length  of  five 
courses,  directly  over  the  place  where  the  fire  had  origi- 
nated. Here  we  found  that  the  cement  had  indeed  filled  all 
vacant  spaces,  but  that  the  timber  was  covered  with  a  layer 
ol  soft  and  brittle  charcoal,  varying  from  one  to  three  inches 
in  thickness. 

There  was  no  other  alternative  now  but  to  go  to  work 
and  cut  in  a  sufficient  number  of  openings,  remove  all  the 
injected  cement,  and  carefully  scrape  the  charcoal  from 
every  burnt  stick  of  timber.  This  task  required  eighteen 
carpenters,  day  and  night,  for  two  months,  beside  the  at- 
tendance of  common  labor,  and  delayed  the  filling  up  of  the 
air  chamber  by  fully  four  weeks.  The  work  was  extremely 
disagreeable  and  unhealthy  ;  men  had  to  lie  for  hours  in 
confined  spots,  without  room  to  turn,  and  breathing  a  foul 
mixture  of  hot  candle-smoke  and  cement-dust  combined 
with  powdered  charcoal,  and  under  pressure  at  that,  the 
temperature  being  eighty  degrees.  In  proportion  as  the 
cement  was  cut  away,  the  full  extent  of  the  fire  gradually 
began  to  dawn  upon  us.  In  place  of  one  opening  in  the 
timber  five  were  required  in  order  to  reach  the  remotest 
points.    They  varied  from  three  to  four  feet  square  in  size. 

Above  the  first  opening  the  fire  had  destroyed  the  third, 
fourth,  and  fifth  course,  having  burned  through  the  tin  which 
lies  between  the  fourth  and  fifth,  and  also  one  or  two  cubic 
feet  of  the  sixth  course.  In  this  latter  course  the  timbers  are 
laid  three  inches  apart  with  concrete  between.  This  con- 
crete checked  all  further  spread  of  the  fire  in  the  sixth  course, 
and  in  every  other  spot,  except  above  the  large  opening,  the 
tin  had  acted  as  an  effective  barrier.  The  fourth  course  under 
the  tin  was  the  principal  sufferer.  The  various  ramifications 
of  the  fire  had  evidently  been  caused  by  air  leaks.  In 
several  places  one  stick  was  burned  away  for  thirty  feet,  and 
the  adjoining  ones  remained  sound.  The  fattest  sticks  had 
succumbed  the  soonest.  Since  the  timber  was  laid  in  courses 
at  right  angles,  there  was  an  opportunity  for  the  fire  to 
branch  off  in  a  zigzag  direction,  leaving  one  stick  and  passing 
off  in  another  course  to  the  right  or  left  and  up  or  down. 
The  general  combustion,  however,  was  of  the  nature  of  a 


57 


slow  charring,  progressing  equally  in  all  directions.  When- 
ever a  stick  was  only  partially  consumed  it  was  carefully 
scraped  and  the  cavity  rammed  full  of  cement.  The  larger 
spaces  were  filled  up  with  yellow  pine  forced  in  with  screw- 
jacks  and  wedges,  in  lengths  of  from  eight  to  ten  feet,  and 
well-bolted  vertically  and  laterally.  Care  was  taken  to  break 
joints  and  to  scarf  as  much  as  possible.  It  was  difficult  to  in- 
troduce larger  timber,  since  it  had  to  be  inserted  into  the 
fourth  course  through  the  openings  cut  from  below.  All 
jagged  burnt  ends  were  cut  to  a  square  face  with  chisels. 
After  everything  was  filled  up  solid,  a  number  of  five-foot 
bolts  were  driven  up  from  below  so  as  to  unite  both  the  old 
and  new  timber  into  a  compact  body. 

Forty  iron  straps  of  4x3-4  iron  were  also  bolted  against 
the  roof  from  below,  so  as  to  balance  the  break  of  bond  in 
the  fourth  course.  In  order  to  further  prevent  any  undue 
settling  over  the  line  of  the  fire,  the  space  beneath  in  the  air- 
chamber  was  built  entirely  of  square  blocks  of  trap-rock, 
carefully  laid  in  cement,  in  place  of  the  gravel  concrete 
which  fills  the  rest  of  the  chamber.  It  must  be  remembered 
that  there  are  still  eleven  courses  of  sound  timber  above  the 
burnt  district.  These  have  abundant  capacity  to  distribute 
any  local  deficiencv  in  equal  bearing.  From  the  faithful  man- 
ner in  which  the  work  was  done  it  is  certain  that  the  burnt 
district  is  fully  as  strong,  if  not  stronger  than  the  rest  of  the 
caisson. 

The  final  repairs  were  concluded  March  6th,  and  the  air 
chamber  completely  filled  March  nth. 

Lighting  of  Caisson. 

The  subject  of  illuminating  a  caisson  in  a  satisfactory  man- 
ner, is  rather  a  difficult  problem  to  solve.  A  powerful  light 
is  of  prime  necessity,  to  overcome  the  want  of  all  reflecting 
surfaces  ;  to  penetrate  the  thick  mist  usually  occupying  such 
places;  and  to  illuminate  every  foot  of  soil  which  was  any- 
thing but  uniform  in  character.  The  burning  of  candles  is 
attended  with  an  intolerable  amount  of  smoke,  resulting  from 
a  rapid  but  incomplete  combustion.  This  nuisance  was  over- 
come somewhat  by  reducing  the  size  of  the  wick,  and  of  the 


58 


candle,  and  by  mixing  alum  with  the  tallow,  and  also  steep- 
ing the  wick  in  vinegar.  The  inhaling  of  so  much  floating 
carbon  is  very  injurious  to  the  lungs,  as  the  lamp-black  re- 
mains in  them  for  weeks  and  months.  Nevertheless  candles 
had  to  be  used  more  or  less  for  all  special  work  requiring 
illumination  close  by.  Lamps  are  of  little  account  since  they 
smoke  more  than  candles,  and  the  oil  is  dangerous  in  case  of 
fire. 

Fortunately,  the  existence  ot  an  establishment  in  NewYork, 
for  the  production  of  oxygen  gas  in  large  quantities,  and  at 
moderate  prices,  made  the  introduction  of  calcium  lights 
quite  feasible. 

For  a  time,  cylinders  filled  with  compressed  oxygen  gas, 
and  compressed  coal  gas,  were  lowered  into  the  caisson  and 
there  used.  The  danger,  however,  of  breaking  a  freshly 
charged  cylinder  was  too  great  on  account  of  the  risk  of  an 
explosion.  A  double  system  of  pipes  was  therefore  put  up 
in  the  air-chamber,  one  for  oxygen  and  the  other  for  coal  gas, 
which  takes  the  place  of  pure  hydrogen.  In  the  end  of  each 
chamber  was  one  burner,  and  a  special  one  next  to  the  water 
shafts,  making  fourteen  calcium  lights  in  all.  In  addition, 
there  were  sixty  burners  for  common  street  gas.  which  was 
used  whenever  the  supply  of  oxygen  failed.  The  two  gas- 
mains  passed  to  the  outside  of  the  caisson,  where  they  con- 
nected with  two  tanks.  In  order  to  make  the  system  effec- 
tive it  was  necessary  to  have  the  gas  pressure  always  one 
pound,  or  thereabouts,  in  excess  of  the  air  pressure  in  the 
caisson,  and  also,  to  maintain  this  as  the  caisson  sank.  For 
this  purpose  the  two  gas  tanks  were  filled  with  water  from 
an  artificial  reservoir,  having  a  head  always  slighly  in  excess 
of  the  caisson  pressure.  Into  these  tanks  the  gases  were  dis- 
charged from  smaller  cylinders,  under  a  pressure  of  two  hun- 
dred and  twenty-five  pounds.  The  immediate  effect  was  to 
force  the  water  trom  them  back  into  the  reservoir,  until  the 
tank  was  full,  when  the  supply  was  stopped.  The  pipes  lead- 
ing to  the  caisson  remained  open,  and  the  gas  passed  through 
them  under  the  pressure  due  to  the  artificial  head  of  water. 
By  means  of  glass  gauges  the  contents  of  the  tanks  could  be 
watched  and  replenished  as  often  as  necessary.    As  the  cais- 


THE    BROOKLYN  FOUNDATION. 


son  sank,  the  reservoir  was  raised  from  time  to  time.  This  was 
rather  troublesome,  and  was  avoided  in  the  New  York  caisson 
by  placing  the  gas  tank  below  in  the  air-chamber,  other- 
wise a  tower  of  eighty  feet  in  height,  would  have  to  be  built 
by  degrees.  The  gases  could,  of  course,  have  been  pumped 
directly  into  the  tanks,  were  it  not  that  the  stroke  of  the 
pump  creates  an  unpleasant  jumping  of  the  flame.  The  oxy- 
gen gas  was  delivered  in  a  compressed  state,  and  the  coal 
gas  was  compressed  on  the  spot.  When  the  oxygen  gas  was 
of  good  quality,  two  calcium  lights  were  sufficient  for  one 
chamber,  one  hundred  and  two  feet  long  by  thirty  feet  wide. 
The  heat  produced  is  less  than  that  of  a  gas  flame,  and  the 
product  of  combustion  water.  One  attendant  was  sufficient 
for  fourteen  lights,  besides  all  the  gas  lights.  The  lime-ball 
requires  occasional  turning,  as  it  wears  away  by  the  action 
of  the  flame,  and  also  requires  frequent  renewal  when  water 
condenses  in  the  pipes.  The  blow-pipe  burners  are  apt  to 
burn  out  and  get  out  of  order.  The  explosive  flame  will  also 
run  back  and  melt  the  rubber  connection.  In  short,  quite  an 
apprenticeship  is  necessary  to  adapt  the  calcium  lights  to  all 
the  new  conditions.  The  only  danger  lies  in  leakage  of  pipes 
and  from  carelessness  in  leaving  cocks  open.  One  gas  explo- 
sion took  place  below,  sufficient  to  singe  off  whiskers  and 
create  some  alarm.  The  sense  of  smell  is  so  blunted  that  the 
leakage  of  coal  gas  is  not  easily  detected.  But  the  ordinary 
gas  lights  were  found  to  be  the  most  economical.  Their  cost 
is  only  one-fifth  of  the  calcium  light,  and  about  one-third  of 
candles.  They  give  all  the  light  that  is  needed,  and  can 
easily  be  located  at  all  points.  They  produce,  however,  an 
intolerable  amount  of  heat,  and  vitiate  the  air  more  than 
candles,  although  producing  but  little  visible  carbon.  The 
gas-burners  kept  the  temperature  below  at  eighty  degrees 
to  eighty-five  degrees.  As  long  as  the  air-pressure  was  so 
irregular,  all  lights  required  careful  attention  and  regulat- 
ing. During  winter,  the  water-pipes  above,  and  the  reser- 
voir, were  kept  from  freezing  by  steam-pipes  laid  alongside. 

The  cost  of  candles,  calcium  lights,  and  gas,  was  about 
five  thousand  dollars,  of  which  candles  cost  more  than  one- 


60  TIIK   BROOKLYN  FOUNDATION. 

half;  not  including  the  necessary  apparatus,  which  in  one 
item  alone  comprised  over  forty  gas  cylinders. 

Organization  of  Working  Force. 

Each  shift  of  men  worked  in  the  caisson  eight  hours  at  a 
time,  the  first  watch  from  six  A.  M.  to  three  I',  til.,  including 
one  hour  for  breakfast  ;  the  next  watch  from  three  P.  If.  to 
eleven  l'.  M.,  including  one  hour  for  supper  ;  then  a  special 
night-gang  from  eleven  P.  M.  to  six  A.  M. 

The  majority  of  the  men  took  their  meals  along  and 
remained  down  the  full  eight  hours  without  any  injury. 

The  two  day-shifts  alternated  from  week  to  week.  They 
consisted  of  one  general  foreman,  six  assistant  foremen  (one 
for  each  chamber),  and  one  hundred  and  twelve  laborers. 
The  special  night-gang  was  composed  of  one  general  fore- 
man, with  two  assistants  and  forty  laborers,  making  a  total 
force  below  of  three  general  foremen,  fourteen  assistants, 
and  two  hundred  and  sixtv-four  laborers.  This  force  was 
constantly  recruited  from  time  to  time,  and  an  inspection  of 
the  time  books  shows  that  two  thousand  five  hundred  dif- 
ferent men  have  worked  in  the  caisson. 

On  deck  there  were  double  shifts  of  engineers  and  fire- 
men to  run  the  excavating  engines,  and  engines  for  running 
the  dirt-cars,  also  two  gangs  for  attending  to  the  dumping 
of  the  latter.  In  addition  there  were  the  engineers  for  the 
air-compressors  and  stone-hoisting  engine,  blacksmiths, 
machinists,  and  gas  men,  one  gang  to  remove  the  boulders 
brought  up  bv  the  buckets.  A  carpenter's  force  of  twenty- 
five  men  and  thirty  men  for  setting  masonry. 

The  total  daily  force  amounted  in  all  to  three  hundred 
and  sixty  men. 

Under  ordinary  circumstances  it  would  have  been 
economical  to  work  three  full  gangs  below  throughout  the 
twenty-four  hours.  The  work,  however,  was  so  severe 
upon  the  dredge  buckets  that  the  night  hours  from  twelve 
to  six  a.  M.  were  devoted  to  repairs,  both  to  the  buckets  as 
well  as  cars,  engines  and  other  machinery.  The  night  gang 
usually  devoted  themselves  to  getting  out  boulders  where 


THE    BROOKLYN    FOUNDATION.  6; 


only  a  few  men  could  work,  or  they  would  run  one  shaft 
alone  or  be  digging  out  the  other  one. 

Two  shanties  were  put  up  provided  with  duly  numbered 
hooks  and  pegs  for  the  men's  clothes,  most  of  which  were 
left  above,  the  temperature  below  being  too  warm.  Rubber 
boots  were  furnished  by  the  company  at  cost  price.  In 
front  of  the  houses  are  sets  of  wash-troughs  with  hot  and 
cold  water. 

As  each  air  lock  held  thirty  men,  two  sets  of  lockings 
were  required  to  let  down  one  hundred  and  twenty.  The 
old  gang  remained  until  relieved  by  the  new. 

No  trouble  was  experienced  in  getting  all  the  labor 
required,  when  one  man  left  a  dozen  were  ready  to  take  his 
place  ;  New  York  in  fact  is  the  best  labor  market  in  the 
country.  There  was  one  small  strike  at  the  beginning,  but 
it  amounted  to  nothing.  The  wages  paid  at  first  were  two' 
dollars  per  day  for  eight  hours'  work.  After  the  caisson 
had  reached  the  depth  of  twenty-eight  feet  the  rate  was  in- 
creased to  two  dollars  and  twenty-five  cents  for  eight  hours' 
work  and  remained  at  that  up  to  the  end.  The  earlier 
stages  of  the  work  were  in  reality  far  more  disagreeable 
than  at  the  end  ;  on  account  of  the  constant  fog  and  influx 
of  water,  whereas  in  the  latter  stages  the  work  was  dry. 

Effect  of  Compressed  Air  and  Other  Causes  Upon 

Health. 

The  depth  reached  by  this  caisson  was  not  sufficient  to 
produce  such  fatal  cases  of  paralysis  as  attended  the  sinking 
of  the  deeper  caissons  at  St.  Louis.  Only  six  men  were 
temporarily  paralvsed,  and  in  each  case  upon  their  first 
visit,  and  after  remaining  but.  a  short  period  of  time.  None 
of  the  old  hands  were  effected  to  any  extent,  even  when  re- 
maining down  eight  hours. 

Inasmuch  as  the  medical  profession  are  as  yet  somewhat 
undecided  in  their  explanations  of  the  real  causie  of  paralysis 
in  compressed  air,  it  was  proposed  in  the  deeper  New  York 
caisson  to  follow  the  course  pointed  out  by  Captain  Eads, 


62 


THE   BROOKLYN  FOUNDATION. 


ot  shortening  the  hours  ot  labor  from  time  to  time  as  the 
case  may  demand  it,  and  thus  reduce  the  period  that  the 
human  system  is  in  contact  with  the  exciting  cause.  It  is 
not  probable  that  paralysis  is  due  to  the  direct  pressure  of 
compressed  air,  otherwise  all  men  would  be  immediately 
affected  alike,  without  exception,  as  all  parts  of  the  body 
must  be  absolutely  permeable.  The  cause  may  perhaps  be 
sought  for  in  the  fact  that  with  each  breath  a  quantity  ol 
oxygen  is  inhaled  from  two  to  three  times  greater  than  that 
inhaled  in  a  normal  atmosphere.  That  the  system  struggles 
against  this  abnormal  state  of  affairs  is  shown  by  the  fact 
that  the  number  of  inhalations  per  minute  is  involuntarily 
reduced  from  thirty  to  fifty  per  cent.  It  follows,  therefore, 
that  the  shorter  the  period  of  exposure  to  compressed  air 
the  less  the  risk. 

On  the  other  hand,  persons  affected  immediately  upon 
emerging  are  usually  somewhat  nervous  and  excited,  which 
incites  excessive  action  of  the  heart,  and  thus  accelerates 
the  general  tendency  to  paralysis.  Violent  exertion,  such 
as  climbing  of  ladders  and  hard  work,  must  be  avoided. 

The  only  other  inconvenience  experienced  in  caisson 
work  is  in  the  temporary  effect  on  the  ears  in  passing 
through  the  air  lock.  A  short  practice,  however,  soon  en- 
larges the  eustachian  tubes,  so  that  by  setting  the  jaws  at  a 
certain  angle  no  effect  whatever  is  felt  on  the  ear  drum. 

As  the  weather  became  colder  the  men  became  subject  to 
cold  and  congestion  of  the  lungs  while  undergoing  the  severe 
change  ot  the  temperature  from  eightv  degrees  to  forty 
degrees,  which  attends  a  passage  out  of  the  air  lock.  A 
simple  and  effective  remedy  was  provided  for  this  by  putting 
in  a  steam  coil  composed  of  six  rings  of  one  inch  pipe, 
lining  the  inside  of  the  lock  and  provided  with  an  outlet  pipe. 
As  soon  as  the  outlet  air  cocks  were  opened,  steam  was 
allowed  to  flow  through  the  coil  with  the  most  satisfactory 
results.  No  reduction  whatever  of  temperature  took  place, 
neither  was  there  any  formation  of  the  disagreeable  mist 
which  otherwise  attends  a  reduction  of  pressure. 

Another  sanitary  measure,  rendered  necessary  by  the 


THE    BROOKLYN  FOUNDATION. 


63 


presence  of  so  large  a  number  of  men  in  a  confined  space, 
was  the  provision  of  a  water  closet  so  arranged  as  to  dis- 
charge its  contents  out  into  the  open  air.  That  some  care 
had  to  be  exercised  in  its  use  will  be  self-evident  to  caisson 
men. 

Masonry. 

Eleven  courses  of  masonry  were  laid,  averaging  from 
twenty-four  to  twenty-eight  inches  high.  Each  course  con- 
tained from  seven  hundred  to  eight  hrndred  cubic  yards  and 
the  size  of  the  stone  varied  from  thirty  to  one  hundred  cubic 
feet.  The  masonry  of  the  first  seven  courses  was  composed 
of  rough  blocks,  all  bedded  to  an  uniform  rise.  The  blocks 
were  all  rectangular  in  shape,  with  the  vertical  faces  trimmed 
down  so  as  not  to  exceed  joints  four  inches  wide  when  laid 
in  the  wall.  The  Kingston  limestone  was  used  alone  for 
these  courses.  They  were  set  in  heavy  beds  of  cement,  and 
all  the  spaces  filled  in  with  cement  or  with  concrete,  when 
the  spaces  were  large  enough  to  admit  of  the  latter.  As  the 
low  water  line  was  approached  granite  was  substituted  on 
the  face  in  place  of  limestone,  the  latter  being  continued  for 
backing. 

Where  the  backing  is  all  cut  and  composed  of  large  blocks, 
such  masonry  can  be  laid  quite  rapidly.  One  whole  course 
has  been  laid  per  week,  notwithstanding  the  drawbacks 
caused  by  the  mud  and  water  from  the  dredges,  and  at  no 
time  was  the  masonry  behind  the  excavation  in  point  of  pro- 
gress. On  the  10th  of  December  the  level  of  the  masonry 
had  arrived  at  ordinary  high  water  level,  and  was  then  sus- 
pended for  the  season  by  the  severity  of  the  weather.  The 
granite  was  furnished  by  Bodwell  &  Webster,  from  the 
Island  quarries  in  Penobscot  Bay,  on  the  coast  of  Maine. 
When  the  regular  masonry  was  laid  oft  it  was  found  that  the 
caisson  had  moved  one  foot  toward  the  river  and  nine  inches 
toward  the  ferry. 

The  stone-setting  machinery  consisted  of  three  boom  der- 
ricks standing  on  the  masonry  with  masts  fifty-five  feet  high 
and  thirty-five  feet  horizontal  booms.  They  controlled  all 
points  of  the  stone-work.    The  guys  were  secured  outside 


64 


THE   BROOKLYN  FOUNDATION. 


and  had  to  be  regulated  from  time  to  time.  In  the  New- 
York  caisson  the  derrick  guys  are  fastened  directly  to  the 
caisson  itself.  The  same  derricks  will  be  used  to  carry  up 
the  tower  masonry  for  about  fifty  feet,  when  they  will  be 
replaced  by  balance  derricks. 

The  stones  were  raised  by  two  engines,  each  working  three 
drums,  controlled  by  friction  gearing.  They  have  given 
perfect  satisfaction,  the  stones  being  handled  with  ease  and 
rapidity,  and  under  complete  control  in  setting. 

DOCK. 

During  the  winter  months,  the  substantial  dock  resting  on 
top  of  the  caisson,  on  the  river  side,  was  completed,  filled 
in,  and  provided  with  a  track,  turn-tables,  and  unloading 
derrick. 

On  the  land  side  the  excavation  has  been  filled  in  level  up 
to  the  masonry. 

When  the  caisson  proper  had  been  filled  in  the  locks  were 
removed,  the  water-shaft  filled,  and  the  sections  above  the 
timber  taken  out.  Next,  the  coffer  dams  inside  the  masonry 
well-holes  were  removed  and  the  mud  dug  out.  No  water 
leaked  through  the  masonry,  but  considerable  fresh  spring 
water  oozed  up  through  the  timber  foundation,  that  w-as 
easily  kept  in  check  by  pumps.  These  well-holes  were  filled 
with  concrete  for  a  height  of  twenty-five  feet,  requiring  five 
hundred  and  fifty  cubic  yards.  For  the  remainder  of  the 
distance,  up  to  the  floor  line,  these  well-holes  remain  open, 
so  as  to  save  masonry. 

General  Dimensions  Brooklyn  Caisson. 


Length  over  all......   168  feet. 

Breadth   102  ,. 

Height  of  air  chamber   o£  ,. 

Total  height  when  launched,   14-$  ,, 

"        "    when  completed   2i£  ,, 

Cubic  feet  of  timber  in  it   1  )  l.ccc  ., 

Weight  of  iron  work   250  tons. 

Launching  weight  of  caisson   3,000  „ 


THE  NEW  YORK  FOUNDATION. 


The  foundation  of  the  New  York  tower  is  located  at  the 
end  of  pier  twenty -nine,  in  deep  water,  at  a  distance  of  four 
hundred  feet  from  the  shore  or  bulk  head  line.  A  front  of 
two  hundred  and  thirty -five  feet  on  the  pier  line  is  taken  up 
by  the  foundation  itself  and  the  enclosure  of  sheet-piling. 

The  position  of  the  tower  was  such  as  to  occupy  the  two 
ferry  slips  of  ,.the  Williamsburg  Ferry  Company,  between 
piers  twenty-nine  and  thirty.  These  slips  had  to  be  vacated 
before  any  work  could  be  done  on  the  foundation  itself. 

Already  in  July,  1870,  negotiations  were  begun  on  the  site, 
for  the  removal  of  the  ferry  to  an  adjoining  slip,  and  also 
for  the  removal  of  a  neighboring  dumping  ground,  which 
would  be  occupied  by  the  ferry.  Possession  was  obtained 
in  April,  1871,  and  the  construction  of  the  new  ferry  slips 
commenced  on  the  part  of  the  Ferry  Company  and  com- 
pleted in  August. 

While  this  work  was  going  on,  a  length  of  one  hundred 
feet  of  the  end  of  pier  twenty-nine  was  removed,  and  the 
operation  of  dredging  a  level  for  the  reception  of  the  caisson 
carried  on. 

The  river  bed  has  a  slope  of  ten  feet  in  'the  width  of  the 
foundation  and  consists  principally  of  black  dock-mud  over- 
laying the  sand,  and  covered  with  sunken  timber-cribs 
filled  with  stone — the  total  quantity  amounting  to  five 
thousand  yards.  No  difficulty  was  experienced  in  dredging 
the  bed  to  a  uniform  level  of  thirty-seven  feet  below  high 
water. 

As  soon  as  the  ferries  were  vacated,  a  pile  bridge  was 
built  connecting  the  foundation  with  the  shore,  and  covering 


E 


66 


a  space  of  over  four  hundred  feet  in  length  and  one  hundred 
and  eighty  in  width.  It  serves  as  it  platform  for  the  storage 
of  material  and  machinery  required  for  the  sinking  of  the 
caisson,  and  is  in  itself  a  work  of  some  magnitude,  requiring 
in  its  construction  over  two  thousand  piles  averaging  fifty 
feet  in  length. 

Borings. 

A  few  borings  were  made  in  icSjo  from  the  end  of 
pier  twenty-nine,  on  the  site  of  the  foundation,  but 
extending  over  only  one-third  of  the  area.  They  struck 
Gneiss  rock  at  a  depth  (if  eighty  to  eighty-two  feet  below 
high  water,  a  much  more  gratifying  result  than  that  derived 
from  the  first  bore-hole,  which  was  made  at  a  point  four 
hundred  teet  from  the  foundation,  and  struck  bed  rock  at  a 
depth  of  one  hundred  and  seven  feet  six  inches. 

Since  then  holes  extended  over  so  limited  a  portion  of  the 
area,  it  was  very  desirable  to  continue  them  over  the  re- 
maining portion  of  the  foundation  as  soon  as  the  adjacent 
ferry-slips  were  vacated. 

This  occurred  at  so  late  a  day  that  only  four  more  bore 
holes  could  be  put  down,  before  the  caisson  was  ready  for 
sinking. 

The  knowledge  derived  from  nine  small  bore-holes  was 
therefore  the  sole  information  we  possessed  of  an  entire  area 
of  17,500  square  feet.  These  holes  being  moreover  confined 
to  the  outer  edges,  left  the  central  portions  a  terra  incognita. 

The  results  showed  an  extreme  difference  in  the  levels  of 
the  bed  rock  of  twelve  feet,  the  hole  of  the  least  depth  touch- 
ing rock  at  eighty  feet  below  high  water,  and  the  deepest  at 
ninety-two  feet. 

The  strata  consisted  in  the  main  of  a  black  mud  deposit  of 
twelve  feet,  followed  by  a  layer  of  coarse  sand  of  six  feet 
which  overlaid  a  gravel  bed  of  the  same  thickness.  Beneath 
the  gravel  appeared  a  very  heavy  deposit  of  quicksand,  vary- 
ing from  fifteen  to  twenty  feet,  according  to  locality,  and 
abounding  with  boulders  in  its  lower  portion,  varying  from 
two  to  five  feet  in  diameter. 

This  quicksand  extended  usually  to  within  a  few  feet  of 


6; 


the  rock,  and  in  some  instances  to  the  rock  itself.  But  the 
immediate  rock  surface  was  covered  with  a  compact  layer 
of  material  through  which  it  was  impossible  to  drive  a  six- 
inch  pipe  without  shattering  it.  To  drive  the  pipe  one  inch 
only,  required  thirty  blows  of  a  five  hundred-pound  hammer, 
falling  from  a  height  of  twenty  feet.  But  even  in  such  ma 
terial  the  quicksand  would  run  into  the  pipe  from  below  and 
fill  it  up  for  several  feet. 

When  the  sinking  of  the  caisson  commenced,  this  question 
still  remained  undecided,  whether  to  go  to  rock  or  remain 
above  it. 

In  case  of  the  former  alternative,  we  had  the  means  at  hand 
for  blasting  the  entire  rock  to  a  level  surface  if  necessary, 
and  of  removing  the  blasted  material,  at  an  additional  ex- 
pense, it  is  true,  of  several  hundred  thousand  dollars  and  six 
months'  more  time. 

Or,  in  case  the  material  on  the  rock  proved  water-tight, 
it  would  be  feasible  to  sink  a  requisite  number  of  smaller 
foundations  to  the  bed  rock,  sufficient  to  hold  the  immediate 
weight  above,  and  then,  by  a  series  of  smaller  coffer-dams  or 
cylinders,  remove  the  remainder  of  the  material  and  thus  get 
a  uniform  mass  of  material  between  the  rock  and  the  roof  of 
the  air-chamber. 

The  only  course,  therefore,  left  open  under  the  circum- 
stances was  to  proceed  with  the  work,  and  when  the  caisson 
had  arrived  within  a  short  distance  of  the  rock,  make  a  suf- 
ficient number  of  soundings,  and  then  determine  upon  a 
course  of  action  when  we  were  face  to  face  with  the  material. 

The  character  of  these  bore-holes  had  also  made  it  appar- 
ent that  any  single  plan  of  operations  would  not  be  adequate 
for  removing  all  the  material  we  would  encounter.  The 
immediate  river  bed  consisted  of  logs  and  loose  dock  stones, 
followed  by  a  sticky,  black  clay. 

These  materials  could  evidently  be  best  removed  by 
dredges  working  in  water  shafts. 

The  river  sand  and  firm  gravel  beneath  would  be  easier 
removed  through  pipes,  either  by  pumps  or  the  air  pressure 
direct. 


68 


THE  NEW  YORK  FOUNDATION. 


The  coarser  gravel,  however,  would  go  to  the  water  shafts  ; 
whereas  the  fine  quicksand  would  again  be  blown  out  through 
pipes,  until  the  preponderance  of  boulders  and  small  rounded 
stones,  compelled  a  recourse  to  the  water  shafts  again,  pro- 
vided any  dredge  whatever  had  the  capacity  to  remove 
stones  imbedded  in  quicksand. 

For  a  direct  removal  of  material  through  locks,  no  special 
means  were  deemed  necessary  beyond  the  ample  facilities 
afforded  by  four  capacious  air  locks  already  at  hand. 

New  York  Caisson. 

The  plans  for  this  caisson  were  perfected  in  the  summer 
of  1870.  A  contract  for  its  construction  was  made  in 
October  with  Messrs.  Webb  &  Bell,  the  builders  of  the 
first  caisson,  the  iron  work  being  done  by  John  Roach  & 
Son,  of  the  Morgan  Iron  Works.  It  was  built  at  the  foot  of 
Sixth  street,  New  York,  the  old  yard  in  Greenpoint  having 
been  abandoned  for  ship  building  purposes. 

A  rather  severe  winter  with  delays  on  the  part  of  the  iron 
work  prolonged  the  completion  of  it  to  the  8th  of  May,  on 
which  day  it  was  launched  with  the  same  success  attending 
the  first  launch.  It  was  then  towed  to  the  Atlantic  Basin, 
where  seven  additional  courses  of  timber  and  concrete  were 
put  on  preparatory  to  its  removal  to  its  permanent  site. 
In  its 

Construction 

this  caisson  is  in  its  general  features  a  duplicate  of  the 
Brooklyn  caisson.  It  is  built  of  yellow  pine  timber,  the 
air  chamber  being  lined  with  a  thin  skin  of  boiler  plate  on 
the  inside.  The  roof  consists  of  five  courses  of  yellow  pine 
sticks,  twelve  inches  square ;  the  inclined  sides  surrounding 
the  air  chamber  are  also  of  yellow  pine,  and  are  nine  and  a 
half  feet  high  on  top,  and  taper  to  a  rounded  cutting  edge 
of  cast  iron  eight  inches  wide  and  enveloped  by  an  armor  of 
boiler  plate. 

The  timbers  in  all  the  courses  are  scarfed  and  bolted  to- 
gether with  screw  bolts  and  drift  bolts.    About  one  hun- 


69 


dred  and  eighty  tons  qf  bolts  were  used  in  the  fastenings. 
The  dimensions  of  the  base  are  one  hundred  and  seventy- 
two  feet  by  one  hundred  and  two  feet,  covering  an  area  of 
seventeen  thousand  five  hundred  and  forty-four  square  feet. 
Its  length  is  four  feet  greater  than  the  Brooklyn  caisson. 

The  Air  Chamber 

has  a  height  of  nine  feet  six  inches,  and  is  divided  into  six 
rooms  by  means  of  five  main  frames.  The  rooms  vary  from 
twenty-five  to  thirty  feet  in  width  by  one  hundred  and  two 
feet  long,  and  are  subdivided  by  lighter  secondary  frames 
running  through  the  middle.  In  addition  there  are  two 
heavy  cross  frames  extending  through  the  whole  length  of 
the  caisson.  The  amount  of  bearing  surface  is  eighteen  per 
cent,  of  the  whole  base,  and  will  be  increased  to  twenty-five 
per  cent,  of  the  whole  base,  by  reason  of  the  sloping  sides, 
in  case  the  caisson  should  sink  into  the  soil  two  feet. 

The  main  frames  are  of  solid  timber  and  four  feet  wide, 
composed  of  two  central  tires  of  horizontal  timber  and 
two  outer  rows  of  posts.  Thev  are  secured  to  the  roof  by 
long  through  bolts,  extending  through  the  lower  three 
courses  of  the  roof,  and  are  heavily  braced  sideways.  The 
ends  of  the  frames  are  secured  to  the  sides  of  the  air  chamber 
by  knees  and  iron  straps.  Each  frame  is  pierced  by  door- 
wavs  of  ample  size  to  afford  communication  between  the  ad- 
joining chambers. 

The  secondary  frames  are  open  work,  composed  of  posts 
and  sills,  and  can  be  strengthened  if  the  necessity  should 
arise.  An 

Iron  Skin 

lines  the  inside  of  the  air  chamber.  The  iron  is  light  boiler 
plates  of  No.  6  gauge.  A  light  iron  was  purposely  selected 
in  order  to  overcome  to  some  extent,  by  its  buckling,  the 
difficulty  arising  from  the  expansion  and  contraction  of  so 
large  a  surface  rigidly  bolted  to  an  unyielding  mass  of  tim- 
ber. In  addition,  a  series  of  expansion  joints  of  angle  iron 
were  put  in  transversely  to  aid  in  taking  up  the  contraction. 
No  trouble  has  been  experienced  from  this  source  since  the 


7o 


launch.  All  spaces  between  the  skin  and  the  timber  have 
been  filled  with  cement. 

The  skin  performs  two  principal  offices — that  of  making 
the  air  chamber  tight;  and,  secondly,  to  protect  the  timber 
above  against  fire.  It  also  adds  to  the  strength  of  the  whole 
structure. 

Inasmuch  as  the  skin  is  pierced  with  six  thousand  bolts, 
besides  its  own  rivets  and  caulking  seams,  it  was  expected 
that  the  leakage  at  first  would  be  considerably  greater  than 
in  a  caisson  made  tight  by  caulking  with  oakum.  The  ex- 
pectation was  more  than  realized,  since  four  air  pumps  were 
required  to  inflate  the  caisson  sufficiently  toentei  it,  whereas 
one  pump  sufficed  for  the  Brooklyn  caisson.  As  soon,  how- 
ever, as  access  was  had  to  the  air  chamber,  the  leaks  were 
easily  stopped,  being  both  audible  as  well  as  readily  acces- 
sible, and  it  is  even  tighter  than  the  Brooklyn  caisson. 

AlR  Locks. 

Two  sets  of  double  air-locks  are  provided,  each  six  and 
one-half  feet  in  diameter  by  eight  feet  in  height,  and  capable 
of  containing  thirty  men;  thus  enabling  the  whole  working 
force  of  one  hundred  and  twenty  men  to  enter  at  one  locking. 
The  locks  are  built  into  the  roof  of  the  caisson — the  lower 
half  projecting  four  feet  into  the  air-chamber,  and  the  upper 
half  communicating  with  a  rectangular  trough  seven  feet 
long,  which  connects  each  pair  of  locks.  This  trough  en- 
larges above  into  a  circular  well  of  boiler  plate  eight  feet  six 
inches  in  diameter,  which  is  carried  up  inside  the  masonry 
as  the  caisson  sinks.  This  style  of  lock  presents  some  advan- 
tages as  well  as  disadvantages,  when  compared  with  the  old 
mode.  Less  time  is  occupied  in  passing  through  a  large 
number  of  men,  and  the  fatiguing  labor  of  climbing  a  high 
vertical  iron  ladder  within  the  compressed  air  is  avoided. 

On  the  other  hand,  the  locks  are  dark  ;  they  are  liable  to 
be  flooded  by  leakage  from  the  well  above,  thus  cutting  off 
both  ingress  and  egress,  and  in  case  of  an  incursion  of  the 
waters  from  below,  the  avenue  of  escape  is  sooner  cut  off. 
Steam  coils  are  provided  for  maintaining  a  uniform  tempera- 
ture when  coming  out  of  the  lock. 


7i 


The  idea  of  placing  the  air-lock  at  the  bottom  of  the  air- 
shaft,  below  the  water  lenaA  i  'jplace  of  above  it,  in  masonry 
caissons,  is  not  new,  having  been  proposed  in  England  as 
long  ago  as  183 1  by  Lord  Cochran,  and  again  by  Win.  Bush 
in  1841,  and  still  later  in  1850  by  G.  Pfannmuller,  of  Mayence. 
It,  nevertheless,  remained  for  Captain  Eads,  in  his  St.  Louis 
caissons,  to  make  the  first  practical  application  of  the  same 
on  a  really  large  scale  in  this  country. 

Excavation  of  Material. 

The  removal  of  the  material  from  the  caisson  is  effected  as 
before,  by  means  of  open  water  shafts  and  the  Cummings' 
dredges.  The  shafts,  however,  in  place  of  being  square,  are 
round,  having  a  diameter  of  seven  feet  nine  inches.  The 
round  form  is  much  better  adapted  to  resist  a  bursting  pres- 
sure in  case  it  is  necessary  to  blow  the  water  out  of  them. 
Since  the  water  shafts  have  to  be  cut  off  when  the  caisson 
arrives  on  the  rock,  they  are  provided  with  caps  and  air- 
locks of  their  own ;  the  old  Brooklyn  locks  being  used  for 
the  purpose.  This  will  give  the  opportunity  of  filling  the 
shafts  under  pressure. 

In  addition,  fifty-eight  iron  pipes,  of  three  and  a  half  and 
four  inches  diameter,  have  been  distributed  throughout  the 
caisson  for  the  purpose  of  sending  out  aay  sand  that  may  be 
fine  enough  to  admit  of  it. 

gThe  fact,  however,  of  three  bore-holes  out  of  four  encoun- 
tering boulders,  made  it  necessary  to  provide  the  means 
used  before  for  their  removal. 

The  Supply  Shafts 

are  four  in  number,  two  of  twenty-one  inch  diameter,  and 
two  of  two  feet  diameter,  disposed  symmetrically  through- 
out the  caisson,  and  arranged  in  the  same  manner  as  those 
used  before.  They  will  prove  more  than  sufficient  to  supply 
all  the  concrete  that  one  hundred  and  twenty  men  can  dis- 
pose of  in  filling  the  air  chamber. 

The  Lighting 
is  done  by  gas  principally,  although  a  double  set  of  pipes  has 
been  put  in  for  sixteen  calcium  lights.    Sixty  double  gas  bur- 


72 


THE  NEW  YORK  FOUNDATION. 


ncrs  have  been  provided,  giving  ten  lights  for  each  chamber. 
The  roof  and  sides  have  also  been  painted  white,  thus  increas- 
ing the  reflecting  surfaces. 

The  management  of  the  gas,  however,  has  been  reversed 
from  the  Brooklyn  arrangement.  In  one  of  the  chambers 
below  are  two  gas  cylinders,  one  for  oxygen,  the  other  for 
hydrogen  gas,  each  six  feet  long,  and  three  feet  six  inches  in 
diameter.  The  gas  pipes  in  the  chamber  connect  with  these 
tanks.  Compressed  gas  is  forced  into  them  through  special 
pipes  leading  down  from  above,  and  the  requisite  excess  of 
pressure  over  the  caisson  pressure,  is  maintained  by  a  head 
of  water  forcing  the  gas  out  of  the  tanks  into  the  pipes.  On 
the  dock  above,  at  an  elevation  of  a  few  feet  above  the  water 
level,  are  the  two  other  cylinders,  the  exact  counterpart  of 
those  below.  They  are  partly  filled  with  water,  which  com- 
municates by  pipes  with  the  lower  tanks,  and  forces  the  gas 
out  of  the  latter.  The  stage  of  water  in  the  upper  tanks  will 
always  indicate  the  amount  of  gas  in  the  lower  tanks,  and  as 
the  caisson  sinks  it,  of  course,  increases  the  head  of  water,  for 
forcing  out  the  gas  in  the  exact  ratio  required.  The  cost  of 
gas  is  only  one-third  that  of  candles,  besides  giving  a  much 
better  light  and  making  no  smoke. 

Sea  Worms. 

Particular  care  has  been  taken  in  this  caisson  to  protect 
the  timber  from  the  sea  worm  on  the  outside.  This  protec- 
tion is  only  required  while  the  caisson  is  afloat  and  while  it 
is  being  sunk — ultimately  all  the  timber  will  be  submerged 
far  below  the  river  bed  where  the  worm  never  penetrates. 
The  borings,  moreover,  showed  that  the  laver  of  gravel 
occurring  twelve  feet  below  the  river  is  permeated  with  fresh 
water  which  is  fatal  to  the  teredo. 

Every  beam  on  the  whole  outside  of  the  caisson  and  also 
on  top  of  the  sixth  roof  course  is  thoroughly  caulked,  both 
with  a  view  to  keep  out  the  salt  water,  as  well  as  to  aid  the 
air-tightness,  and  to  relieve  the  iron  skin  from  any  back 
pressure. 

In  the  next  place  the  same  surface  is  heavily  graved  with 


THE  NEW  YORK  FOUNDATION. 


a  composition  of  coal  tar,  rosin  and  dydraulic  cement,  the 
latter  material  having  sufficient  body  and  grit  to  dull  the 
boring  apparatus  of  the  teredo.  Coal  tar  alone  has  but  little 
efficacy,  because  the  animal  does  not  digest  the  material 
through  which  it  bores. 

Over  this  coating  there  extends  an  unbroken  sheet  of  heavy 
tin,  covering  the  outside  and  the  top  of  the  sixth  course. 
Every  seam  is  soldered  air-tight,  and  a  layer  of  tar  paper 
put  above  and  below  the  tin.  On  the  outside  of  this  is 
the  four  inch  yellow  pine  sheathing  of  the  caisson  which  has 
been  creosoted  with  ten  pounds  of  oil  to  the  cubic  foot. 

These  precautions  will  not  seem  superfluous  when  it  is 
remembered  that  the  young  sea-worm  is  a  microscopic 
animal,  less  than  the  sixteenth  of  an  inch  in  diameter,  and  can 
penetrate  any  crevice  that  water  can  pass  through. 

The  course  above  this  is  also  caulked  and  is  protected  on 
the  outside  like  the  lower  courses. 

We  are  thus  provided  with  an  additional  air-tight  layer  in 
the  caisson,  which  will  come  into  play  in  case  of  accident  to 
the  iron  skin. 

The  seven  courses  of  timber  immediately  following  the 
caisson  proper  are  all  laid  with  cement  spaces  between  the 
timber ;  they  are  surrounded  by  tarred  sills,  and  the  tin  and 
creosoted  sheathing  is  carried  up  outside  the  whole  extent. 
The  courses  above  that  are  completely  enveloped  in  concrete. 

Floor. 

The  caisson  was  launched  with  a  temporary  floor,  ex- 
tending over  the  entire  base.  This  was  made  necessary  by 
reason  of  the  shallow  water  in  front  of  the  launching  ways. 
This  floor  remained  in  until  the  caisson  was  permanently 
grounded  on  the  river  bed,  and  helps  materially  in  main- 
taining a  level  position  of  the  same. 

The  air-chamber  was  not  inflated  before  the  caisson  had 
touched  bottom,  and  enough  masonry  laid  to  prevent  its 
rising  at  high-tide  from  the  effect  of  the  air  pressure.  This 
floor  then  came  into  play  to  distribute  uneven  pressures 
until  access  was  had  to  the  air-chamber  and  the  work  of 
excavating  was  commenced. 


74 


Table  of  Quantities. — New  York  Caisson. 

Length  over  all   172  feet. 

Breadth   102  '' 

Height   14    "  6  inches. 

Area  of  base   1 7, 5  54  square  feet. 

Quantity  of  timber   ...    1 18,000  cubic  feet. 

Weight  of  bolts   180  tons. 

Weight  of  iron  work ....    200  " 

Launching  weight  of  caisson   3>25°  " 

Preparations  for  Sinking  the  Caisson. 

Owing  to  the  vexatious  delays  in  obtaining  possession  of 
the  ferry  slips  adjoining-  pier  twenty-nine,  nothing  of  any  im- 
portance could  be  done  in  the  matter  of  locating  machinery 
or  workshops  until  August,  when  the  ferry-boats  finally 
ceased  running  into  their  old  slips,  and  the  new  boundary 
line  was  established  between  the  property  of  the  Ferry 
Company  and  the  Bridge  Company. 

The  month  of  August  and  part  of  September  were  em- 
ployed in  building  a  pile  dock  from  the  bulkhead  line  out  to 
the  caisson,  averaging  four  hundred  and  fifty  feet  in  length 
and  one  hundred  and  eighty  feet  in  width,  inclusive  of  the 
old  pier. 

At  its  outer  end  was  formed  a  scpiare  inclosure,  open  on 
the  river  side,  for  the  purpose  of  receiving  the  caisson  when 
it  was  readv  to  be  towed  up  from  the  Atlantic  Basin.  • 

The  amount  of  space  on  the  pier  line  was  so  scant,  that  a 
narrow  platform  of  ten  feet  width  constituted  all  the  avail- 
able room  between  the  sides  of  the  caisson  and  the  fender 
rack  of  the  ferry  on  the  one  side,  and  the  crowded  shipping 
of  the  adjoining  slip  on  the  other,  showing  that  economy  of 
space  during  erection  is  not  the  least  of  the  merits  of  caisson 
foundations. 

Inclosure  of  Caisson. 
For  the  purpose  of  obtaining  still  water,  the  caisson  was 
surrounded  by  a  wall  of  sheet  piling,  composed  of  white  pine 
plank  fifty  feet  long  and  six  inches  thick*  This  served  to 
break  the  force  of  the  tidal  current,  which  often  runs  at  the 
rate  of  four  miles  per  hour,  and  would  produce  a  pressure 
of  ninetv  tons  against  the  structure  at  a  time  when  it  is  most 


THE  NEW  YORK 


FOUNDATION. 


75 


important  to  have  it  stationary  in  its  true  position — just 
before  touching  bottom. 

This  entire  work  of  pile-driving  and  dock-building  was 
superintended  in  the  most  efficient  manner  by  Mr.  George 
McNulty. 

Within  the  enclosure  thus  formed  the  bottom  was  dredged 
to  a  uniform  level  of  thirty-seven  feet  below  high  water,  by 
means  of  the  clam-shell  dredge  of  Messrs.  'Morris  &  Cura- 
mings,  who  did  this  portion  of  the  work  under  contract. 

They  removed  in  all  seven  thousand  yards  of  material,  of 
which  one  thousand  five  hundred  yards  consisted  of  dock 
stone  and  logs. 

Machinery  and  Workshops. 

On  the  pile  platform  thus  prepared  were  erected  two 
engine  houses  for  the  dredge  machinery,  which  was  trans- 
ferred from  the  Brooklyn  side,  and  had  been  enlarged  to 
correspond  to  the  increased  depth  to  which  this  caisson 
would  go. 

Two  double  hoisting  engines  were  set  up,  both  for  un- 
loading stone  and  setting  stone  on  the  caisson. 

Four  additional  double  engines  were  provided  for  unload- 
ing sand,  gravel,  coal,  cement,  and  lumber,  for  hauling 
dredge  cars  back  and  forth,  pumping  gas  and  mixing  con- 
crete. 

The  principal  budding,  however,  was  the 

Compressor  House, 

for  supplying  air  to  the  caisson. 

The  air-pumping  machinery  comprised  thirteen  of  the 
Burleigh  rock  drill  air  compressors,  ranged  in  a  single  row, 
each  discharging  its  air  into  one  common  ten-inch  main 
overhead,  and  provided  with  suitable  valves  to  shut  it  off 
from  the  main  system. 

Every  compressor  has  its  own  steam  boiler  of  the  vertical 
tubular  type,  so  connected  as  either  to  work  independently 
or  as  an  entire  set.  Pumps  for  cooling  the  air  were  also  in 
duplicate. 


76  THE  NEW  YORK  FOUNDATION. 

Six  of  these  compressors  were  brought  from  the  Brooklyn 
caisson,  the  remaining  seven  being  purchased  anew. 

From  the  compressor  house  the  air  was  carried  by  a  ten- 
inch  cast-iron  pipe  through  an  intermediate  air  reservoir, 
for  a  distance  of  one  hundred  and  fifty  feet  under  the  dock, 
to  the  caisson,  whence  two  branches  of  six-inch  rubber  hose 
continued  it  by  means  of  the  supply  shafts  to  the  air  chamber 
below. 

The  idea  governing  the  general  arrangement  of  the  air 
pumps  was  the  necessity  of  an  uninterrupted  supply  of  air, 
day  and  night,  for  at  least  a  year,  under  a  constantly  in- 
creasing duty. 

This  could  only  be  done  by  a  number  of  smaller  machines, 
so  that  if  one  were  out  of  repair  the  remainder  would  have 
sufficient  capacity  for  the  work. 

Besides  the  buildings  for  machinery  and  offices,  a  number 
of  sheds  were  erected  for  the  accommodation  of  black- 
smiths, carpenters,  machinists,  for  cement  and  for  general 
stores;  also  wash-room,  clothes-houses,  hospital,  and  rest- 
ing-rooms  for  the  caisson  men. 

Three  unloading  derricks,  a  double  railroad  track,  and 
two  overhanging  platforms  comprised  the  preparations  on 
the  dock  for  supplying  the  caisson  derricks  with  stone. 

Towing  the  Caisson  into  Position. 

All  preparations  for  receiving  the  caisson  being  com- 
pleted by  September  11,  it  was  on  that  day  towed  from  the 
Atlantic  basin  to  its  final  resting-place.  While  at  the  basin, 
seven  additional  courses  of  timber  and  concrete  had  been 
built  upon  it  under  contract  with  Mr.  D.  Burtis,  Junior. 
All  the  outer  seams  were  caulked  and  protected  by  felt,  tin, 
and  creosoted  sheathing.  The  various  pipes,  shafts,  and 
locks  were  also  carried  up  to  the  necessary  height. 

This  work  was  very  carefully  attended  to  under  direction 
of  Colonel  Paine. 

Four  air  pumps  and  boilers  placed  on  the  deck  served  to 
inflate  the  structure  during  the  voyage.  Its  draft  of  water 
when  empty  was  twenty-three  feet,  reduced  by  inflation  to 
seventeen. 


THE  NEW  YORK  FOUNDATION. 


77 


Total  weight,  seven  thousand  tons. 

Under  the  skillful  guidance  of  Captain  Murphy,  and  the 
assistance  of  six  tugs,  the  trip  was  safely  performed  in  two 
hours  and  a  half.  A  few  days'  work  then  sufficed  to  com- 
plete the  pile  inclosure  and  confine  the  New  York  caisson 
in  its  permanent  position. 

Additional  Timber  Courses. 

By  the  ist  of  November  the  last  of  the  timber  courses 
was  laid  under  the  Burtis'  contract. 

The  great  timber  foundation  was  now  complete  !  It 
contains  twenty-two  feet  of  solid  timber  above  the  roof  of 
the  air  chamber,  seven  stories  more  than  the  Brooklyn 
caisson,  and  since  the  strength  of  such  structures  varies  as 
the  square  of  the  depth,  we  may  consider  it  to  be  nearly 
twice  as  strong  as  its  Brooklyn  brother. 

The  result  has  proved  this.  At  a  depth  of  seventy-eight 
feet,  and  a  load  on  its  back  of  fifty-three  thousand  tons,  not 
the  slightest  sign  of  weakness  or  crippling  has  been  dis- 
covered !  No  deflection  has  been  observed  in  the  roof, 
even  when  the  main  frames  and  edges  below  were  entirely 
dug  out  and  not  resting  on  the  ground.  The  principal 
object  of  these  frames  is,  at  most,  a  precautionary  one, 
besides  serving  to  fill  up  the  air-chamber  to  the  extent  of 
their  bulk. 

Outer  Coffer-Dam. 

An  outer  coffer-dam  has  been  carried  up  outside  of  the 
masonry.  It  is  composed  of  upright  posts  12x12  placed  four 
feet  apart,  with  an  outer  planking  of  white  pine  six  inches 
thick.  Shores  extend  from  each  post  to  the  masonry,  ar- 
ranged in  tiers  for  every  three  courses  of  stone. 

The  coffer-dam  commences  seven  feet  below  the  upper 
course  of  timber,  where  it  is  attached  to  the  caisson  by  a 
heavy  creosoted  sill  and  screw-bolts.  The  space  between  it 
and  the  timber  is  filled  with  concrete,  fourteen  feet  in  height, 
beneath  which  the  outer  covering  ol  tin  extends  for  five  feet. 
The  upper  layer  of  timber  is  covered  with  three  and  one-half 
feet  of  concrete,  amounting  in  all  to  three  thousand  five  hun- 
dred yards. 


78 


THE  NEW  YORK  FOUNDATION. 


Under  certain  circumstances  it  would  have  been  possible 
to  omit  this  coffer-dam  and  save  the  considerable  expense 
attending  it.  On  the  Brooklyn  foundation  no  ojjter  coffer- 
dam was  used,  the  depth  of  water  being  too  shallow. 

In  any  case  it  was  necessary  to  carry  up  the  dam  for  a 
height  of  twenty-five  feet.  When  the  last  course  of  timber 
was  laid,  the  caisson  was  still  floating  two  feet  from  the  bot- 
tom at  low  water,  and  ten  feet  at  extreme  high  water.  To 
keep  it  on  the  bottom  at  extreme  high  water  required  four 
courses  of  masonry,  and  when  inflated  with  air,  three  ad- 
ditional courses  were  required. 

Owing  to  the  rise  and  fall  of  the  tide  and  the  great  top- 
weight  of  the  structure,  the  requisite  buoyancy  and  stability 
could  only  be  attained  by  the  displacement  of  a  coffer-dam, 
especially  as  the  usual  appliances  of  suspended  screws  for 
keeping  the  structure  level  when  afloat  were  obviously  in- 
applicable. 

It  had  also  been  intended  to  surround  the  tower  by  a  per- 
manent dock  of  stone  and  concrete,  the  foundations  of  which 
could  now  be  laid  within  this  coffer-dam  at  a  moderate  ex- 
pense. This  intention  was,  however,  abandoned  owing  to 
the  necessity  of  strictly  confining  the  expenditure  of  money 
to  the  bridge  proper.  At  present  the  coffer-dam  has  been 
designedly  filled  up  with  sand,  and  forms  part  of  the  timber 
dock  extending  to  the  tower  masonry. 

It  will'last  for  fifteen  years  without  renewal. 

The  coffer-dam  also  formed  a  protection  to  all  the  caisson 
pipes,  and  made  it  possible  to  repair  them  when  out  of  order. 

These  pipes  consist  of  four  supply  shafts  of  two  feet  diame- 
ter, and  fifty  pipes  of  four  inches  and  three  and  a  half  inches. 
None  of  them  were  built  in  the  masonry,  but  came  up  be- 
tween the  Avail  and  the  coffer-dam. 

On  one  occasion,  through  the  accident  of  a  large  stone  fall- 
ing, a  supply  shaft  was  broken  off  at  the  timber-line,  and 
would  have  been  lost  but  for  the  coffer-dam.  But  the  chief 
benefit  derived  from  it  was  the  fact  that  the  masonry  was  laid 
below  the  water  during  the  most  of  the  winter.  The  work 
of  sinking  the  caisson  could,  therefore,  proceed  uninterrupt- 


THE  NEW  YORK  FOUNDATION. 


79 


edly,  no  matter  if  the  masonry  stopped  on  account  of  the 
cold  weather. 

Inner  Coffer-Dams. 

Two  smaller,  inner  coffer-dams  served  as  a  water-tight 
lining-  to  the  main  well  holes  of  the  masory.  Within  them 
were  carried  up  the  sections  of  water  shaft,  as  well  as  curb- 
ing- of  the  air-lock  shafts. 

As  far  as  the  timber  extends,  this  curbing  consists  of  a 
boiler-plate  shell,  stiffened  by  flanges  and  secured  to  the 
timber  by  wood-screw  bolts.  The  wooden  curbing  of  six- 
inch  plank  was  notched,  dowelled,  caulked,  and  further  pro- 
tected on  the  outside  by  a  ring  of  concrete  between  it  and 
the  inner  coffer-dam.  The  leakage  has  been  practically 
none. 

Derricks  and  Masonry. 

The  stones  were  laid  by  three  boom  derricks,  similar  to 
those  employed  on  the  Brooklyn  foundation.  They  were 
guyed  solely  from  the  caisson  itself,  so  that  the  settling  of 
the  latter  did  not  disturb  the  guys.  Every  twenty-feet  the 
derricks  had  to  be  raised,  an  operation  requiring  a  few  days. 

Twenty-five  courses  of  stone  have  been  laid  on  top  of  the 
timber,  making  a  height  of  fifty  feet,  and  amounting  in  all  to 
eleven  thousand  seven  hundred  cubic  yards  of  masonry. 

The  stones  are  all  bedded  down  to  a  uniform  rise  in  one 
course,  with  joints  dressed  down  to  moderate  projections, 
the  rise  varying  from  twenty  to  thirty  inches.  Both  granite 
and  limestone  were  used  indiscriminately,  the  former  coming 
principally  from  Maine,  and  the  latter  from  Kingston,  Lake 
Champlain,  and  Cacajoharie. 

Owing  to  the  early  commencement  of  winter,  much  of  the 
stone  in  transit  lor  the  New  York  tower,  was  frozen  in,  and, 
in  order  to  keep  on  setting,  it  became  necessary  to  use  all 
the  backing  intended  for  the  Brooklyn  tower.  This  has  been 
supplied  since,  and  at  no  time  has  there  been  any  stoppage 
for  want  of  stone. 

During  the  severest  weather,  work  was  suspended  for 
several  days  at  a  time,  the  coffer-dam  preventing  the  river 
from  covering  the  wall. 


8o 


THE  NKW  VOKK  FOUNDATION. 


Work  in  the  Air  Chamber. 

By  the  end  of  November  sufficient  weight  had  been  placed 
on  the  caisson  to  prevent  its  rising  for  a  short  time  at  low 
tide  when  inflated. 

A  gang  of  laborers  worked  for  several  hours  every  day, 
taking  up  the  floor  of  the  air  chamber  and  removing  the 
principal  obstructions  in  the  shape  of  dock  logs  and  stones 
under  the  edges  and  frames. 

In  proportion  to  the  weight  above,  the  length  of  time 
spent  below  was  increased,  until  two  regular  gangs  were  at 
work,  four  hours  on  and  four  hours  off,  the  caisson  being 
now  permanently  grounded. 

Each  gang  consisted  of  about  seventy  laborers  and  seven 
foremen.  In  a  short  time  an  extra  night  gang  was  also 
established.  Two  weeks  were  consumed  in  removing  and 
taking  out  the  floor. 

This  floor  proved  a  valuable  adjunct  in  giving  the  caisson 
a  level  bed  on  which  to  rest,  and  in  preventing  it  from 
tipping  up  on  either  end  before  sufficient  weight  had  been 
placed  on  it. 

The  character  of  the  work  at  this  particular  time  was 
more  disagreeable  than  at  any  subsequent  period.  This 
location  had  for  many  years  been  the  site  of  the  principal 
dumping-ground  for  city  garbage.  The  mud  abounded  in 
decaying  animal  and  vegetable  remains.  Although  the  odor 
of  these  was  checked  while  imbedded  in  the  salt  water  mud, 
it  came  forth  in  its  original  strength  when  brought  in  con- 
tact with  the  caisson  air.  More  men  were  overcome  by  foul 
air  than  by  compressed  air. 

By  keeping  the  material  constantly  covered  with  water, 
so  as  to  cover  the  odor,  it  was  gradually  disposed  of  through 
the  water  shafts. 

This  black  dock  mud  is  really  a  clay,  and  is  the  silt  brought 
down  bv  the  North  River,  merely  lacking  time  and  pressure 
to  make  it  as  hard  and  tenacious  as  ordinary  clays.  It 
derives  its  black  color  from  sewer  discharges,  but  is  by  no 
means  their  product. 

The  coarse  river  sand  and  beach  gravel  beneath  the  mud 


THE  NEW  YORK  FOUNDATION. 


Si 


soon  created  a  change  for  the  better  below.  The  water  was 
easily  expelled  by  the  air,  leaving  it  dry  under  foot. 

By  this  time  also  the  gas-lights  were  in  complete  opera- 
tion in  all  the  chambers,  giving  ample  light  in  every  part. 
Two  coats  of  whitewash  over  the  roof  and  walls  aided  in 
reflecting  it  and  making  the  air  chamber  an  agreeable  spot 
compared  with  what  it  was  at  the  beginning. 

The  performance  of  the 

Dredges 

in  the  mud  and  coarse  sand  and  gravel  was  very  satisfac- 
tory. They  constantly  maintained  a  hole  about  six  feet  in 
depth  under  the  water  shafts,  and  removed  from  three  hun- 
dred to  four  hundred  yards  per  day. 

Water  for  the  shafts  was  supplied  by  two  sets  of  four-inch 
pipes,  one  of  fresh  water  from  the  city  mains,  the  other  con- 
necting with  a  force  pump  on  the  dock,  which  threw  in 
a  constant  supply  of  salt  water  under  great  pressure,  and 
proved  of  considerable  use  subsequently  in  loosening  boul- 
ders under  the  water  shafts.  Owing  to  the  fact  that  the 
shafts  were  fifty  feet  from  the  nearest  edge  of  the  caisson,  a 
supply  of  water  from  the  river  without  could  at  no  time  be 
relied  upon. 

Throwing  Out  Sand  Through  Pipes. 

About  fifty  pipes  were  located  in  the  roof  of  the  cais- 
son, passing  up  through  the  timber,  and  discharging  above 
beyond  the  coffer-dam.  In  size  they  varied  from  three  and 
a  half  to  four  inches. 

The  precise  mode  in  which  they  were  to  be  utilized  in 
throwing  out  sand  had  been,  to  a  certain  degree,  left  unde- 
termined. Two  modes  were  applicable,  either  to  throw  out 
the  sand  by  direct  force  of  air,  or  else  have  recourse  to  sand 
pumps. 

Very  satisfactory  experiments  had  been  made  the  year  be- 
fore in  the  Brooklyn  caisson  in  throwing  out  sand  through 
pipes  by  air  pressure. 

The  same  mode  had  been  used  ten  years  previously  by 
General  S.  Smith  and  Mr.  C.  C.  Martin  in  blowing  sand  out 


82 


THE  NEW  YORK  FOUNDATION. 


of  cylinders,  and  more  recently  at  Omaha  under  similar  con- 
ditions. 

The  apparatus  is  very  simple,  consisting  merely  of  a 
piece  of  pipe  and  a  through  way  cock  extending  into  the 
air  chamber. 

Moreover,  the  objection  of  a  very  small  air  space  to  draw 
upon,  as  is  the  case  in  pneumatic  cylinders,  would  not  apply 
in  a  large  caisson,  which  constitutes  a  large  reservoir  in  it- 
self, and  would  retard  any  rapid  fall  of  pressure. 

Another  strong  reason  in  favor  of  the  air  process  was  this  : 
An  air-chamber  with  an  iron  skin  can  be  made  practically 
air-tight,  but  a  certain  quantity  of  air  must  be  thrown  in  per 
minute  to  keep  the  air  fresh  and  fit  to  live  in.  This  air  would 
usually  escape  under  the  edges  and  do  no  work.  Now,  why 
not  allow  it  to  escape  through  pipes  and  at  the  same  time 
carry  out  sand  with  it,  and  not  be  wasted?  There  was 
ample  air-pump  power,  thirteen  compressors  having  been 
provided,  of  which  number  four  only  were  required  to  sup- 
ply the  leakage,  but  six  to  supply  sufficient  fresh  air. 

Any  other  mode,  however,  of  sending  out  the  material 
would  require  extensive  provision  of  machinery  in  the  shape 
of  pumps,  boilers,  and  pipes,  entailing  an  additional  cost  of 
at  least  $40,000,  and  difficult  of  application  for  want  of  the 
required  space  around  the  foundation. 

In  view  of  these  considerations,  it  was  first  determined  to 
give  the  air  system  a  thorough  trial. 

The  result  has  been  eminently  satisfactory.  At  a  depth  of 
sixty  feet  sand  was  discharged  through  a  three  and  one-half 
inch  pipe  continuously  for  half  an  hour  at  the  rate  of  one 
yard  in  two  minutes.  This  represents  the  labor  of  fourteen 
men  standing  in  a  circle  around  the  pipe  and  shoveling  as 
fast  as  their  strength  would  permit.  At  this  depth  the  sup- 
ply of  air  was  sufficient  to  supply  three  pipes  at  a  time.  This 
may  appear  a  small  number  compared  with  the  whole  num- 
ber of  pipes,  but  yet  was  enough  to  keep  at  least  sixty  men 
busy. 


THE  NEW  YORK  FOUNDATION. 


83 


The  labor  in  itself  is  very  fatiguing,  making  frequent  rest- 
ing spells  necessary  ;  more  hands  are  required  to  throw  the 
sand  to  the  pipes  than  to  feed  them,  and  a  large  proportion 
of  labor  is  expended  in  digging  out  under  the  frames  and 
edges. 

The  most  economical  mode  of  working  these  pipes  was 
made  the  subject  of  many  trials  by  Col.  Paine  and  Mr.  Col- 
lingwood,  the  engineers  in  charge  in  the  caisson.  Trials 
were  first  made  with  flexible  pieces  of  hose  provided  with 
strainers  at  the  end.  These  became  choked  too  easily  both 
in  the  holes  of  the  strainer  and  in  the  hose.  The  strainer 
was  then  removed  and  a  shorter  piece  of  vertical  hose  used, 
in  connection  with  a  piece  of  iron  pipe.  This,  in  turn,  was 
discarded  for  a  stationary  iron  pipe,  extending  within  a 
foot  of  the  ground  and  provided  with  a  stop-cock  below 
the  roof. 

Around  the  lower  end  of  this  pipe  the  sand  and  earth 
were  heaped  up  in  shape  of  a  cone,  while  another  workman 
attended  to  the  opening  or  shutting  of  the  air  cock. 

As  the  pressure  increased,  the  lower  orifices  of  the  pipes 
were  reduced  to  three  inches  and  finally  two  inches,  the 
same  quantity  being  discharged  with  a  smaller  loss  of  air. 

The  material,  of  course,  passes   out   with  tremendous* 
velocity,  stones  and  gravel  being  often  projected  at  least 
four  hundred  feet  high.    When  the  feeding  below  was  too 
slow  or  irregular,  the  sand  would  be  thrown  very  high,  but, 
by  practice,  the  discharge  became  more  uniform. 

In  order  to  deflect  the  sand  at  the  top  of  the  pipe  at 
right  angles,  both  wrought  and  cast  iron  elbows  were  used 
at  first.  The  sand  blast  would  generally  cut  through  these 
in  an  hour  or  tw  o,  sometimes  in  a  few  minutes,  the  thick- 
ness of  iron  being  one  and  a  half  inches.  That  .portion  of 
the  elbow  struck  by  the  sand  was  then  made  open  and  pro- 
vided w  ith  a  thick  cap  of  chilled  Franklinite  iron,  capable 
of  being  reversed  when  worn  on  one  spot.  These  would  at 
most  last  two  days.  Finally  all  elbows  were  taken  off, 
heavy  granite  blocks  placed  over  the  mouth  of  the  pipes, 


84 


TDK  NEW  YORK  FOUNDATION. 


and  the  material  discharged  against  them  into  the  coffer- 
dam. 

Several  minor  casualties  occurred  from  the  discharge  of 
stones,  such  as  a  boatman  on  the  river  having  his  finger 
shot  off  and  a  laborer  being  shot  through  the  arm  by  a 
large  fragment. 

Some  inconvenience  was  experienced  from  the  wearing 
out  of  the  ends  of  the  pipes  below  in  the  air  chamber.  The 
cocks  also  wore  out  rapidly,  owing  to  careless  attendance 
in  not  opening  them  all  the  way.  The  pipes  in  the  timber 
did  not  jjwear.  When  a  four-inch  pipe  had  become  cut,  a 
three  and  a  half-inch  pipe  was  driven  inside  of  it,  then  a 
three-inch,  and  at  last  a  two-inch.  But  they  lasted  so  well 
on  an  average,  that  one-third  of  the  pipes  were  never  used. 

Quicksand. 

When  the  quicksand  was  fairly  entered  upon,  it  was  found 
that  the  dredge  buckets  no  longer  operated  to  any  advantage. 
This  sand,  in  combination  with  small  stones  and  boulders, 
will  compact  to  a  mass  as  hard  as  rock,  which  cannot  be 
penetrated  by  the  teeth  of  a  bucket,  and  even  the  point  of  a 
crowbar  can  scarcely  be  driven  into  it. 

Some  slight  relief  was  experienced  by  the  use  of  a  hose 
under  the  shaft  to  stir  up  the  material,  but  even  then  the 
sand  was  so  fine  as  to  escape  through  the  crevice  in  the 
buckets. 

The  sand  pipes  became  henceforth  the  sole  reliance,  and 
answered  admirably,  until  the  coarse  gravel  and  stones 
became  so  plentiful  as  to  choke  the  ends  of  the  pipes,  making 
it  necessary  to  stop  for  a  moment  to  remove  the  stone. 

The  work  of  the  last  ten  feet,  from  sixty-eight  to  seventy- 
eight,  was,  on  this  account,  very  tedious  and  slow.  Previous 
to  this  the  progress  had,  at  times,  averaged  a  foot  per  day  ot 
sixteen  hours,  implying  the  removal  of  six  hundred  and  fifty 
yards  per  day,  but  toward  the  end  this  rate  decreased  to  one 
or  two  feet  per  week. 


THE  NEW  YORK  FOUNDATION. 


85 


Cutting  off  the  Water  Shafts. 

At  a  depth  of  sixty-eight  teet  a  number  of  boulders  were 
encountered  under  one  water-shaft,  too  large  to  be  moved 
either  by  the  dredge  or  by  outside  appliances.  It  therefore 
became  necessary  to  cap  the  shaft  and  blow  out  the  water, 
similar  to  the  operation  so  frequently  performed  in  Brook- 
lyn. On  top  of  the  cast-iron  cap  was  placed  one  of  the  old 
air-locks,  so  as  to  afford  access  into  the  shaft  thereafter. 

After  the  water  was  blown  out  and  boulders  removed,  the 
shaft  was  cut  off  near  the  roof  of  the  air-chamber.  The  same 
process  was  repeated  with  the  other  shaft.  During  this  time 
the  caisson  was  kept  from  sinking  by  banking  up  the  frames 
and  edges  with  earth. 

The  air  pressure  against  the  caps  of  the  shafts  was  one 
hundred  and  thirty-three  tons.  The  individual  sections  had 
been  tested  to  twice  this  pressure  before,  but  by  way  of  pre- 
caution an  additional  dead  weight  of  fifty  tons  was  placed  on 
them. 

Where  water  shafts  are  used,  it  is  absolutely  necessary  to 
make  provisions  for  capping  them. 

Soundings  for  Rocks. 

At  a  depth  of  seventy  feet,  soundings  were  begun  in  the 
air-chamber  for  the  location  of  bed  rock,  by  means  of  a  point- 
ed rod,  ten  feet  long,  driven  in  by  sledges. 

A  trial  was  made  to  sound  by  means  of  a  pipe  and  water 
jet,  but  was  abandoned  on  account  of  the  numerous  stones. 
These  probings  were  carried  on  daily  for  a  month,  until  a 
clear  idea  of  the  form  and  depth  of  bed-rock  was  attained. 

The  surface  was  evidently  very  irregular,  composed  of 
alternate  projections  and  depressions,  the  extreme  difference 
in  elevations  encountered  being  sixteen  feet,  and  occurring 
chiefly  along  the  water  edge.  Throughout  the  central  por- 
tion, however,  and  covering  at  least  two-thirds  of  the  entire 
area,  the  irregularities  were  much  less,  amounting  to  only 
three  or  four  feet  in  a  length  of  one  hundred  and  sixty,  and 
width  of  about  seventy-five  feet. 


86 


Till.  \K\Y  YORK  FOUNDATION. 


The  caisson  would  apparently  settle  on  a  broken  ridge  of 
rock,  running  diagonally  from  one  corner  to  the  other,  and 
having  a  moderate  clip  of  perhaps  five  feet  in  the  hundred 
toward  the  land  ;  but  falling  off  very  suddenly  toward  the 
east  corner  in  number  one  chamber. 

With  these  facts  before  us,  it  was  evident  that  it  would  be 
a  matter  of  immense  expense  and  great  loss  of  time  to  blast 
down  the  rock  to  a  comparatively  level  surface;  but  unless 
this  was  done,  it  would  appear  equally  dangerous  to  all  the 
caisson  to  rest  on  the  rock  at  one  end  and  not  on  the  other. 

Fortunately  one  circumstance  put  a  more  favorable  appear- 
ance upon  the  case,  and  that  was  that  the  top  of  the  rock 
was  found  to  be  covered  for  a  depth  of  two  to  four  feet  by  a 
layer  of  very  compact  material,  so  hard  that  it  was  next  to 
impossible  to  drive  in  an  iron  rod  without  battering  it  to 
pieces. 

Moreover,  where  the  rock  lay  the  lowest,  this  layer  of 
hard  material  had  its  greatest  thickness. 

It  was  good  enough  to  found  upon,  or  at  any  rate  nearly 
as  good  as  any  concrete  that  could  be  put  in  place  of 
it.  In  extent  it  covered  fully  three-fourths  of  the  caisson, 
leaving  a  narrow  strip  of  quicksand  along  the  land  edge,  and 
a  triangular  portion  over  part  of  number  one  and  six 
chamber. 

Since  the  lower  line  of  quicksand  sloped  at  the  rate  of  six 
feet  in  the  hundred,  it  became  necessary  to  penetrate  about 
five  feet  into  the  hard  ground  on  the  water  edge  before  the 
bottom  of  the  quicksand  was  reached  on  the  land  side.  The 
number  of  boulders  found  in  it  was  very  large,  much  greater 
than  were  found  in  the  same  space  on  the  Brooklyn  side. 

It  was  determined  to  rest  the  caisson  on  this  material  at  a 
depth  of  seventy-eight  feet.  The  projecting  peaks  of  bed 
rock  which  already  made  their  appearance  at  seventy-five 
feet,  were  blasted  down  for  some  distance  under  the  shoe, 
and  covered  with  a  foot  of  compressible  earth. 

In  number  six  chamber  a  trench  was  sunk  through  the 
remaining  quicksand  under  the  edge,  and  filled  with  con- 


THE  NEW  YORK   FOUNDATION.  87 


crete  to  confine  the  portion  remaining  within  ;  a  task  of  no 
small  difficulty,  owing  to  the  influx  of  water  and  sand. 

Any  other  small  irregularities  will  be  fully  equalized  by 
the  great  timber  platform  above. 

Bed-rock. 

The  first  spurs  of  bed-rock  were  encountered  at  a  depth 
of  seventy-five  feet,  under  the  shoe  on  the  water-side.  It 
would  seem  that  the  caisson  had  been  scraping  along  a 
vertical  wall  of  rock  for  the  previous  five  feet  at  that  spot. 

The  rock  is  the  ordinary  Gneiss  found  on  Manhattan 
Island  with  a  dip  almost  vertical.  No  part  of  its  surface 
shows  the  rounding  action  of  water  or  ice.  On  the  con- 
trary, the  outcrop  is  in  the  form  of  sharp  thin  ridges,  with 
steep  vertical  sides  occurring  in  parallel  ranges. 

On  such  a  bottom  no  sliding  can  ever  take  place,  no  matter 
what  the  average  slope  might  be.  At  78  feet  the  outcrop 
was  struck  in  a  number  of  places  and  blasted  down  a  short 
distance  below  the  edge.  A  slight  covering  of  soil  gave  the 
necessary  amount  of  compressible  material  above  these 
rocky  points.  Nearly  all  of  them  occurred  under  the  edge 
oh  the  water-side,  a  favorable  circumstance,  since  the  re- 
sultant of  pressure  is  in  that  direction. 

No  fresh  water  was  found  on  the  rock,  but  salt  water  en- 
tered upon  a  reduction  of  air  pressure. 

Effects  of  the  Compressed  Air  on  the  Men. 

These  were  not  so  serious  as  first  anticipated.  The  few 
cases  of  death  that  occurred  could  in  but  two  instances  be 
charged  to  the  direct  effects  of  pressure. 

As  the  latter  increased,  the  working  hours  below  were 
gradually  reduced  from  four  hours  to  two  hours,  twice  a 
day,  at  thirty-five  pounds.  It  is  true  that  scarcely  any  man 
escaped  without  being  somewhat  affected  by  intense  pain  in 
his  limbs  or  bones  or  by  a  temporary  paralysis  of  arms  and 


88 


II  IK  NEW  YORK  FOUNDATION. 


legs,  but  they  all  got  over  it,  either  by  suffering  for  a  few 
days  outside,  or  by  applying  the  heroic  mode  of  returning 
into  the  caisson  at  once,  as  soon  as  the  pains  manifested 
themselves,  and  then  coming  out  very  slowly.* 

The  shortening  of  the  hours  of  labor  produced  the  best 
results  in  keeping  the  men  in  good  condition,  but  even  this 
was  not  necessary  for  all  constitutions,  because  some  could 
remain  below  with  impunity  for  six  hours  at  the  highest 
pressure. 

After  the  Locks  were  passed  the  men  had  their  choice  of 
coming  up  either  by  an  elevator  or  by  circular  stairs. 

During  the  winter  months  all  tendency  to  congestion  of 
the  lungs,  owing  to  the  sudden  change  of  temperature  in 
coming  out  of  the  locks,  was  controlled  by  means  of  steam 
coils  in  the  latter,  so  arranged  as  to  warm  the  air  when 
coming  out  of  the  lock  and  to  cool  it  when  passing  in. 

The  general  condition  of  the  air  below  was  very  pure, 
due  to  the  absence  of  candles  and  illumination  by  gas  alone. 

Mr.  Collingwood  found  that  as  the  pressure  increased  the 
gas-burners  gave  more  light,  and  at  thirty-five  pounds  a 
one-foot  burner  gave  as  much  light  as  a  four-foot  burner 
outside.  We  therefore  had  a  maximum  production  of  light 
with  a  minimum  production  of  irrespirable  gases. 

The  services  of  Dr.  A.  H.  Smith  were  engaged  for  the 
purpose  of  attending  to  all  caisson  cases  and  examining  new 
candidates  for  work  below.    He  has  been  quite  successful  in 


*  Amony  the  numerous  explanations  offered,  as  to  the  causes  of  these  pains,  the 
most  satisfactory  one  seems  to  be  that  of  Prof.  Rameaux.  of  Strasburg,  in  whose  opinion 
these  accidents  are  due  to  the  fact  that  the  normal  gases  of  the  blood  (carbonic  acid, 
oxygen  and  nitrogen),  dissolve  themselves  to  a  high  degree  under  the  influence  of  ex- 
treme pressure,  and  return  into  a  gaseous  state  as  soon  as  the  pressure  is  reduced  to  one 
atmosphere,  obstructing  the  views  and  exposing  the  patient  to  the  same  dangers  that 
would  be  produced  by  an  injection  of  air  into  the  veins. 

A  rather  severe  personal  experience  of  the  writer,  resulting  from  a  stay  of  several 
hours  in  the  New  York  caisson,  would  seem  to  confirm  the  above  view  to  some  extent. 
Relief  from  the  excruciating  pain  was  afforded  in  his  case  by  a  hypodermic  injection  of 
morphine  in  the  arm,  where  the  pain  was  most  intense,  and  a  further  stupefaction  by 
morphine,  taken  for  twenty-four  hours  internally  until  the  pains  abated. 


THE  NEW  YORK  FOUNDATION. 


89 


his  treatment,  and  it  is  to  be  hoped  that  his  experience  will 
be  made  public  for  the  benefit  of  future  works. 

The  fact  remains,  however,  that  the  effects  of  compressed 
air  on  the  human  system  constitute  the  principal  difficulty 
attending  deep  pneumatic  foundations.  Men  are  somewhat 
difficult  to  get,  wages  are  high,  and  the  time  of  labor  be- 
comes so  short  that  the  work  must  necessarily  be  done  un- 
der a  disadvantage  and  under  an  immense  amount  of  super- 
vision, where  it  is  at  all  difficult  or  different  from  ordinary 
digging  in  a  uniform  material. 

Besides  two  general  foremen  and  fifteen  under-bosses,  it 
required  the  daily  attendance  of  both  Col.  Paine  and  Mr. 
Collingwood,  assisted  occasionally  by  Mr.  Martin  and  Mr. 
McNulty,  to  keep  matters  moving  smoothly  below  and  in 
conjunction  with  affairs  above. 

An  ingenious  mechanical  telegraph,  contrived  by  Col. 
Paine,  proved  of  great  assistance  in  keeping  up  communica- 
tion between  the  upper  and  lower  world. 

Gas. 

The  ordinary  street  gas  has  been  the  only  agent  used  for  il- 
lumination. Sixty  burners,  divided  among  the  six  chambers, 
gave  all  the  light  required.  The  gas  was  burned  under  a 
pressure  of  one  or  two  pounds  in  excess  of  the  caisson  pres- 
sure, and  was  at  all  times  uniform  and  plentiful  in  supply. 

A  gas  pump  above  forced  the  gas  steadily  into  the  tank 
below,  and  as  the  latter  would  fill  with  gas  it  raised  the 
column  of  water  in  the  tank  above,  where,  at  a  certain  stage, 
a  float  controlled  the  throttle-valve  of  the  gas  pump,  and 
thus  regulated  the  supply  of  gas  within  restricted  limits, — the 
whole  arrangement  being  self-acting. 

One  interesting  fact  was  observed  which  may  possibly  be 
new,  and  that  is,  that  in  compressed  air  all  gas-lights  become 
sensitive  flames,  answering  to  the  stroke  of  a  hammer  on  a 
piece  of  iron,  or  even  to  tones  of  the  voice. 


90  THE  NEW  YORK  FOUNDATION. 


Movements  of  the  Caisson. 

The  downward  movement  of  the  eaisson  has  been  under 
perfect  control  throughout  the  whole  of  the  sinking.  It 
usually  occurred  at  low  tide  and  was  very  gradual,  owing 
principally  to  the  wide  frames  and  broad  shoe. 

While  the  caisson  was  passing  through  the  mud,  river 
sand,  and  gravel,  the  frames  sank  through  the  material  with- 
out digging,  but  in  the  quicksand  and  harder  material  below, 
the  whole  frames  had  to  be  dugout  underneath  before  settle- 
ment would  take  place. 

The  caisson  also  sank  perpendicularly  in  its  true  place,  no 
movement  occurring  in  any  direction.  This  result  was 
principally  owing  to  the  facility  with  which  it  was  kept  level 
by  digging. 

The  side  friction  was  considerable,  but  difficult  to  estimate, 
because  the  frames  and  shoe  were  seldom  entirely  clear.  It 
could  not  have  been  less  than  six  hundred  pounds  per  square 
foot  of  external  surface,  varying  with  the  amount  of  air  pas- 
sing out  under  the  shoe. 

The  total  resistance  offered  by  the  side  friction  is,  however, 
quite  small  when  compared  with  the  total  bulk.  At  a  depth 
of  seventy-eight  feet  the  side  friction  amounted  to  six  thou- 
sand tons,  whereas  the  weight  of  the  whole  foundation,  in- 
cluding masonry,  was  fifty-three  thousand  tons. 

At  seventy-eight  feet  the  excess  of  the  downward  pressure 
of  the  caisson  over  the  upward  pressure  of  the  air  at  low 
tide  would  average  from  ten  to  twelve  thousand  tons,  not 
including  side  friction.  The  air  pressure  has,  however,*  fre- 
quentlv  run  so  low  as  to  give  an  excess  of  downward  pres- 
sure of  fifteen  thousand  tons.  An  excess  of  overweight  is 
in  all  cases  an  advantage,  as  it  saves  considerable  digging. 

The  experience  with  this  foundation  goes  to  show  that  a 
larger  caisson  is  much  easier  to  handle,  is  safer  and  under 
more  perfect  control  than  a  smaller  one.  The  labor  question, 
however,  becomes  the  most  serious  drawback  where  a  con- 
siderable number  of  men  have  to  be  brought  together  under 


THE  NEW  YORK  FOUNDATION. 


abnormal  circumstances.  The  forces  of  nature  may  be 
measured  and  brought  under  control,  provided  they  are 
properly  understood,  but  human  nature  is  not  so  amenable 
to  laws. 

Filling  of  Air-Chamber  &  Completion  of  Foundation. 

The  concrete  for  filling  the  chamber  is  all  mixed  above 
and  let  down  through  the  supply  shafts  ready  for  distribu- 
tion below. 

No  brick  pillars  were  used  as  under  the  Brooklyn  caisson, 
the  bearings  of  the  frames  being  so  wide  as  to  be  equal  to 
all  contingencies  when  once  uniformly  packed  under  with 
concrete.  Enough  stones  and  earth  were  left  below  to  re- 
duce the  amount  of  concrete  required  to  3,300  yards,  about 
the  same  amount  as  in  the  Brooklyn  caisson.  The  filling  in 
took  place  in  such  a  manner  as  to  leave  the  final  exit  by 
means  of  the  water-shafts  ;  all  the  remaining  quicksand  was 
dug  out  below,  down  to  the  hard  pan  and  worked  up  into 
the  concrete. 

In  six  weeks  after  commencing  the  filling  in  there  remain- 
ed only  two  hundred  and  eighty  yards,  showing  an  average 
of  nearly  one  hundred  yards  per  dav. 

By  July  20th  the  water  shafts  were  finally  filled,  the  air 
pressure  taken  off,  and  the  locks  on  the  water  shafts  removed 
Several  trials  were  made  to  take  off  the  air  pressure  before 
the  filling  was  complete,  but  the  water  invariably  came  in 
when  the  pressure  was  reduced  below  thirty  pounds.  Up 
to  the  end  as  many  as  five  air  pumps  were  needed  mainly 
because  the  concrete  was  so  easily  traversed  by  the  air. 
Another  month  was  consumed  in  removing  the  water  shafts, 
air  shafts,  inner  cofferdam,  and  outer  shores,  and  in  filling 
the  two  large  well  holes  with  concrete,  as  well  as  the  other 
shafts  and  smaller  pipes,  and  in  completing  the  dock  around 
the  tower.  The  laying  of  stone  was  resumed  before  the  air 
chamber  was  entirely  filled. 

The  New  York  foundation  was  now  finished. 


92 


THE  NEW  YORK  FOUNDATION. 


CONCLUDING  REMARKS. 

The  pleasant  task  remains  yet  ot  expressing  my  thanks  to 
the  gentlemen  w  ho  have  so  ably  assisted  in  the  prosecution 
of  the  work,  and  to  whose  untiring  industry,  constant  watch- 
fulness and  sound  judgment,  is  mainly  due  the  success  which 
has  attended  it  to  the  present  time. 

The  work  in  both  caissons  has  been  carried  on  under  the 
daily  supervision  of  Col.  Paine  and  Mr.  Collingwood,  relieved 
at  times  by  Mr.  Martin  and  Mr.  McNulty,  whenever  the  nu- 
merous outside  duties  of  these  latter  gentlemen  would 
permit. 

The  labor  below  is  always  attended  with  a  certain  amount 
of  risk  to  life  and  health,  and  those  who  face  it  daily  are, 
therefore,  deserving  of  more  than  ordinary  credit. 

The  general  foremen  below  have  been  Messrs.  Young, 
Clarke,  Creene,  Woliver  O'Malley.and  Korner,  assisted  by 
twelve  under  foremen. 

The  masonry,  carpentry,  and  machine  departments  have, 
throughout,  been  most  efficiently  attended  to  by  Messrs. 
Douglass,  Farrington,  and  Smith:  while  the  draughting- 
room  has  been  in  charge  of  Mr.  Hildenbrandt,  and  occasion- 
ally Mr.  Yonder  Bosch. 

To  Mr.  Horatio  Allen,  consulting  engineer,  my  acknow- 
ledgments are  due  for  his  counsel  and  advice. 

In  regard  to  the  relations  of  the  engineering  department 
and  the  general  management,  it  gives  me  pleasure  to  bear 
testimony  that  all  requisitions  from  the  engineer  department 
have  been  met  with  the  utmost  promptness,  both  in  respect 
to  quantity  as  well  as  quality,  and  that  the  relations  of  the 
different  executive  branches  have  been  conducted  with  a 
mutual  co-operation,  conducive  to  the  highest  results,  both 
in  efficiency  and  economy. 


N 

i 


DIMENSIONS. 
Length  168  Feel 

Breadth  102 
Height  14  74  „ 

Height  of  Air  Chamber  9  Vs  „ 


BROOKLYN  CAISSON. 
EAST  RIVER  BRIDGE. 

Enqineer   W.  A.  ROEBLING. 


CONTENTS. 
Cubic  Feet  Timber  110.  000 

Tons  Iron  230 
Launching  Weight  (Tons)  3  000 
Launched   March  1870. 


AVERY 


PLAN 

of  the 

BROOKLYN  CAISSON 

oj    12*^  course 


I6S  Ft* 


BROOKLYN  CAISSON 
LONGITUDINAL  SECTION 

through  centre. 


N.Y.  CAISSON 
HORIZONTAL  SECTION 


at  Top  of  Air  Chamber 


fr£.  frtt 


Ri'rtr  Side  if  Cat's tan 


N  Y. CAISSON 
LONGITUDINAL  SECTION 


10  Feet  From  Edge 


N.Y.  CAISSON 
TRANSVERSE  SECTION. 

through  air  locks  . 
Engineer   W.  A.  ROEBLING. 


BROOKLYN  TOWER 

Oct.  1872 
ENGINEER. W.A  ROEBLING 


